diff --git a/README.md b/README.md
index d9654ff..d54f0f9 100644
--- a/README.md
+++ b/README.md
@@ -130,6 +130,7 @@ See `config/agents.example.json` for the full schema. Key fields:
       "model": "claude-sonnet-4-6",
       "toolPolicy": "readonly",
       "replyMode": "direct",       // reply in-place
+      "maxBudgetUsd": null,       // disable SDK budget limit; use a number to cap cost
       "persona": "./personas/assistant.md",
       "knowledge": ["team.md"]
     },
@@ -156,6 +157,7 @@ All options are documented in `.env.example`. Key ones:
 | `ANTHROPIC_API_KEY` | Yes | Anthropic API key |
 | `FEISHU_EVENT_MODE` | No | `websocket` (default) or `webhook` |
 | `DEFAULT_WORK_DIR` | No | Root directory for projects (default: parent of cwd) |
+| `CLAUDE_MAX_BUDGET_USD` | No | Per-query SDK budget in USD; set `off`, `false`, `none`, `disabled`, or `0` to omit it |
 | `ALLOWED_USER_IDS` | No | Comma-separated Feishu open_ids (empty = allow all) |
 | `OWNER_USER_ID` | No | Admin user with full permissions |
 | `MEMORY_ENABLED` | No | Enable long-term memory system |
diff --git a/src/__tests__/config-loader.test.ts b/src/__tests__/config-loader.test.ts
index 7951997..93bc6c7 100644
--- a/src/__tests__/config-loader.test.ts
+++ b/src/__tests__/config-loader.test.ts
@@ -71,6 +71,13 @@ describe('AgentConfigFileSchema', () => {
     expect(result.success).toBe(false);
   });
 
+  it('accepts null maxBudgetUsd to disable budget', () => {
+    const result = AgentConfigFileSchema.safeParse({
+      defaults: { maxBudgetUsd: null },
+      agents: [{ id: 'test', maxBudgetUsd: null }],
+    });
+    expect(result.success).toBe(true);
+  });
   it('rejects zero maxTurns', () => {
     const result = AgentConfigFileSchema.safeParse({
       agents: [{ id: 'test', maxTurns: 0 }],
diff --git a/src/__tests__/config.test.ts b/src/__tests__/config.test.ts
index fb3696a..b0b880b 100644
--- a/src/__tests__/config.test.ts
+++ b/src/__tests__/config.test.ts
@@ -49,6 +49,24 @@ describe('config', () => {
       const { config } = await loadConfig();
       expect(config.claude.toolTimeoutSeconds).toBe(1200);
     });
+
+    it('should parse CLAUDE_MAX_BUDGET_USD as a number', async () => {
+      vi.stubEnv('CLAUDE_MAX_BUDGET_USD', '12.5');
+      const { config } = await loadConfig();
+      expect(config.claude.maxBudgetUsd).toBe(12.5);
+    });
+
+    it('should disable CLAUDE_MAX_BUDGET_USD when set to off', async () => {
+      vi.stubEnv('CLAUDE_MAX_BUDGET_USD', 'off');
+      const { config } = await loadConfig();
+      expect(config.claude.maxBudgetUsd).toBeUndefined();
+    });
+
+    it('should disable CLAUDE_MAX_BUDGET_USD when set to 0', async () => {
+      vi.stubEnv('CLAUDE_MAX_BUDGET_USD', '0');
+      const { config } = await loadConfig();
+      expect(config.claude.maxBudgetUsd).toBeUndefined();
+    });
   });
 
   describe('defaults', () => {
diff --git a/src/agent/__tests__/config-loader.test.ts b/src/agent/__tests__/config-loader.test.ts
index cf8dec9..74902c9 100644
--- a/src/agent/__tests__/config-loader.test.ts
+++ b/src/agent/__tests__/config-loader.test.ts
@@ -410,4 +410,20 @@ describe('maxBudgetUsd / maxTurns fallback', () => {
     const { agentRegistry } = await import('../registry.js');
     expect(agentRegistry.get('pm')!.maxBudgetUsd).toBe(100);
   });
+  it('should let file-level null maxBudgetUsd disable SDK budget', async () => {
+    await setupWithClaudeConfig(
+      { defaults: { maxBudgetUsd: null }, agents: [{ id: 'pm' }] },
+      { maxBudgetUsd: 50 },
+    );
+    const { agentRegistry } = await import('../registry.js');
+    expect(agentRegistry.get('pm')!.maxBudgetUsd).toBeUndefined();
+  });
+  it('should let agent-level null maxBudgetUsd override defaults and config', async () => {
+    await setupWithClaudeConfig(
+      { defaults: { maxBudgetUsd: 20 }, agents: [{ id: 'pm', maxBudgetUsd: null }] },
+      { maxBudgetUsd: 50 },
+    );
+    const { agentRegistry } = await import('../registry.js');
+    expect(agentRegistry.get('pm')!.maxBudgetUsd).toBeUndefined();
+  });
 });
diff --git a/src/agent/config-loader.ts b/src/agent/config-loader.ts
index 7ab06a9..7bc9d28 100644
--- a/src/agent/config-loader.ts
+++ b/src/agent/config-loader.ts
@@ -75,6 +75,16 @@ function resolveToolPolicy(policy: ToolPolicyValue | undefined): {
 }
 
 // ─── Merge 逻辑 ────────────────────────────────────────────
+function resolveMaxBudgetUsd(input: AgentConfigInput, defaults: AgentDefaults): number | undefined {
+  if (input.maxBudgetUsd !== undefined) {
+    return input.maxBudgetUsd === null ? undefined : input.maxBudgetUsd;
+  }
+  if (defaults.maxBudgetUsd !== undefined) {
+    return defaults.maxBudgetUsd === null ? undefined : defaults.maxBudgetUsd;
+  }
+  return config.claude.maxBudgetUsd;
+}
+
 
 /**
  * 合并单个 agent 配置：input → defaults → 内置默认值
@@ -92,7 +102,7 @@ function mergeAgentConfig(input: AgentConfigInput, defaults: AgentDefaults): Age
     toolPolicy,
     readOnly,
     settingSources: (input.settingSources ?? defaults.settingSources ?? BUILTIN_DEFAULTS.settingSources!) as ('user' | 'project')[],
-    maxBudgetUsd: input.maxBudgetUsd ?? defaults.maxBudgetUsd ?? config.claude.maxBudgetUsd,
+    maxBudgetUsd: resolveMaxBudgetUsd(input, defaults),
     maxTurns: input.maxTurns ?? defaults.maxTurns ?? config.claude.maxTurns,
     requiresApproval: input.requiresApproval ?? defaults.requiresApproval ?? BUILTIN_DEFAULTS.requiresApproval!,
     replyMode: input.replyMode ?? defaults.replyMode ?? BUILTIN_DEFAULTS.replyMode! as 'direct' | 'thread',
diff --git a/src/agent/config-schema.ts b/src/agent/config-schema.ts
index 1713c47..31c04e9 100644
--- a/src/agent/config-schema.ts
+++ b/src/agent/config-schema.ts
@@ -23,6 +23,9 @@ const ToolPolicyDetailedSchema = z.object({
 
 /** toolPolicy 支持两种格式 */
 export const ToolPolicySchema = z.union([ToolPolicySimpleSchema, ToolPolicyDetailedSchema]);
+/** 单次 query 最大花费 (USD)；null 表示不向 SDK 传 maxBudgetUsd */
+const MaxBudgetUsdSchema = z.number().positive().max(1000).nullable();
+
 
 // ─── 飞书账号 ────────────────────────────────────────────────
 
@@ -66,7 +69,7 @@ export const AgentConfigInputSchema = z.object({
   /** Settings 源 */
   settingSources: z.array(z.enum(['user', 'project'])).optional(),
   /** 单次 query 最大花费 (USD)，上限 1000 */
-  maxBudgetUsd: z.number().positive().max(1000).optional(),
+  maxBudgetUsd: MaxBudgetUsdSchema.optional(),
   /** 单次 query 最大轮次，上限 10000 */
   maxTurns: z.number().int().positive().max(10000).optional(),
   /** 是否需要写权限审批 */
@@ -91,7 +94,7 @@ export const AgentDefaultsSchema = z.object({
   model: z.string().optional(),
   toolPolicy: ToolPolicySchema.optional(),
   settingSources: z.array(z.enum(['user', 'project'])).optional(),
-  maxBudgetUsd: z.number().positive().max(1000).optional(),
+  maxBudgetUsd: MaxBudgetUsdSchema.optional(),
   maxTurns: z.number().int().positive().max(10000).optional(),
   requiresApproval: z.boolean().optional(),
   replyMode: z.enum(['direct', 'thread']).optional(),
diff --git a/src/agent/types.ts b/src/agent/types.ts
index 84749b9..cf19595 100644
--- a/src/agent/types.ts
+++ b/src/agent/types.ts
@@ -47,8 +47,8 @@ export interface AgentConfig {
   readOnly: boolean;
   /** 加载哪些 settings 源 */
   settingSources: ('user' | 'project')[];
-  /** 单次 query 最大花费 (USD) */
-  maxBudgetUsd: number;
+  /** 单次 query 最大花费 (USD)。省略表示不向 SDK 传 maxBudgetUsd */
+  maxBudgetUsd?: number;
   /** 单次 query 最大轮次 */
   maxTurns: number;
   /** 是否需要写权限审批（non-owner 场景） */
diff --git a/src/claude/__tests__/executor.test.ts b/src/claude/__tests__/executor.test.ts
index 789d0e3..b5de384 100644
--- a/src/claude/__tests__/executor.test.ts
+++ b/src/claude/__tests__/executor.test.ts
@@ -226,6 +226,25 @@ describe('ClaudeExecutor', () => {
       expect(opts.maxTurns).toBe(5);
       expect(opts.maxBudgetUsd).toBe(0.5);
     });
+
+    it('should omit maxBudgetUsd when config disables it', async () => {
+      const { config } = await import('../../config.js');
+      const prevBudget = config.claude.maxBudgetUsd;
+      config.claude.maxBudgetUsd = undefined;
+      try {
+        await executor.execute(makeInput());
+        const opts = mockQuery.mock.calls[0][0].options;
+        expect(opts).not.toHaveProperty('maxBudgetUsd');
+      } finally {
+        config.claude.maxBudgetUsd = prevBudget;
+      }
+    });
+
+    it('should omit maxBudgetUsd when caller explicitly disables it', async () => {
+      await executor.execute(makeInput({ maxBudgetUsd: undefined }));
+      const opts = mockQuery.mock.calls[0][0].options;
+      expect(opts).not.toHaveProperty('maxBudgetUsd');
+    });
   });
 
   describe('killSessionsForChat', () => {
diff --git a/src/claude/executor.ts b/src/claude/executor.ts
index 00c502e..1b6db72 100644
--- a/src/claude/executor.ts
+++ b/src/claude/executor.ts
@@ -648,6 +648,9 @@ export class ClaudeExecutor {
       readOnly, images, documents,
     } = input;
 
+    const hasMaxBudgetUsdOverride = Object.prototype.hasOwnProperty.call(input, 'maxBudgetUsd');
+    const effectiveMaxBudgetUsd = hasMaxBudgetUsdOverride ? maxBudgetUsd : config.claude.maxBudgetUsd;
+
     const startTime = Date.now();
     const abortController = new AbortController();
     const idleTimeoutMs = (input.timeoutSeconds ?? config.claude.timeoutSeconds) * 1000;
@@ -1041,7 +1044,7 @@ export class ClaudeExecutor {
 
         // 预算和限制 — 默认值从 config 读取，调用方可覆盖
         maxTurns: maxTurns ?? config.claude.maxTurns,
-        maxBudgetUsd: maxBudgetUsd ?? config.claude.maxBudgetUsd,
+        ...(effectiveMaxBudgetUsd !== undefined ? { maxBudgetUsd: effectiveMaxBudgetUsd } : {}),
 
         // 会话续接
         ...(effectiveResumeId ? { resume: effectiveResumeId } : {}),
diff --git a/src/claude/types.ts b/src/claude/types.ts
index 7539df2..dceff94 100644
--- a/src/claude/types.ts
+++ b/src/claude/types.ts
@@ -91,7 +91,7 @@ export interface CompactResult {
 export interface ExecuteOptions {
   /** 覆盖默认 maxTurns (默认 50) */
   maxTurns?: number;
-  /** 覆盖默认 maxBudgetUsd (默认 5) */
+  /** 覆盖默认 maxBudgetUsd；显式传 undefined 表示不向 SDK 传预算限制 */
   maxBudgetUsd?: number;
   /** 不注入 setup_workspace MCP tool (restart 时使用) */
   disableWorkspaceTool?: boolean;
diff --git a/src/config.ts b/src/config.ts
index efbb938..cb422f9 100644
--- a/src/config.ts
+++ b/src/config.ts
@@ -13,6 +13,26 @@ export function parsePositiveInt(raw: string | undefined, fallback: number): num
   return Number.isFinite(n) && n > 0 ? n : fallback;
 }
 
+/**
+ * CLAUDE_MAX_BUDGET_USD 解析：
+ * - 未设置/空字符串：使用 fallback
+ * - off/false/none/disabled/0：关闭 SDK maxBudgetUsd，不向 SDK 传该字段
+ * - 正数：启用预算熔断
+ */
+export function parseOptionalMaxBudgetUsd(raw: string | undefined, fallback: number): number | undefined {
+  const value = raw?.trim();
+  if (!value) return fallback;
+
+  const normalized = value.toLowerCase();
+  if (['off', 'false', 'none', 'disabled', 'disable'].includes(normalized)) {
+    return undefined;
+  }
+
+  const n = Number(value);
+  if (n === 0) return undefined;
+  return Number.isFinite(n) && n > 0 ? n : fallback;
+}
+
 function parseGroupConfigs(raw?: string): Record<string, GroupConfig> {
   if (!raw?.trim()) return {};
   try {
@@ -91,8 +111,8 @@ export const config = {
     effort: (process.env.CLAUDE_EFFORT || 'xhigh') as 'low' | 'medium' | 'high' | 'xhigh' | 'max',
     /** 单次 query 最大轮次 (Agent ↔ Tool 来回次数)，兜底防死循环 */
     maxTurns: parseInt(process.env.CLAUDE_MAX_TURNS || '500', 10),
-    /** 单次 query 最大花费 (美元)，真正的费用熔断 */
-    maxBudgetUsd: parseFloat(process.env.CLAUDE_MAX_BUDGET_USD || '50'),
+    /** 单次 query 最大花费 (美元)。设置 CLAUDE_MAX_BUDGET_USD=off/false/none/disabled/0 可关闭 */
+    maxBudgetUsd: parseOptionalMaxBudgetUsd(process.env.CLAUDE_MAX_BUDGET_USD, 50),
   },
 
   // 工作区配置
diff --git a/src/feishu/event-handler.ts b/src/feishu/event-handler.ts
index f8dcce5..5fe2c02 100644
--- a/src/feishu/event-handler.ts
+++ b/src/feishu/event-handler.ts
@@ -1444,7 +1444,7 @@ async function handleSlashCommand(
       `**工具策略**: ${agentCfg?.toolPolicy ?? '(默认)'}`,
       `**回复模式**: ${agentCfg?.replyMode ?? '(默认)'}`,
       `**需要审批**: ${agentCfg?.requiresApproval ? '是' : '否'}`,
-      `**预算**: $${agentCfg?.maxBudgetUsd ?? '?'} / ${agentCfg?.maxTurns ?? '?'} turns`,
+      `**预算**: ${agentCfg ? (agentCfg.maxBudgetUsd === undefined ? '关闭' : '$' + agentCfg.maxBudgetUsd) : '?'} / ${agentCfg?.maxTurns ?? '?'} turns`,
     ];
 
     if (agentCfg?.editablePathPatterns?.length) {
@@ -2799,7 +2799,7 @@ export async function executeClaudeTask(
       readOnly,
       model: agentCfg?.model,
       maxTurns: agentCfg?.maxTurns,
-      maxBudgetUsd: agentCfg?.maxBudgetUsd,
+      ...(agentCfg ? { maxBudgetUsd: agentCfg.maxBudgetUsd } : {}),
       settingSources: agentCfg?.settingSources,
       toolAllow: agentCfg?.toolAllow,
       toolDeny: agentCfg?.toolDeny,
@@ -2950,7 +2950,7 @@ export async function executeClaudeTask(
         readOnly,
         model: agentCfg?.model,
         maxTurns: agentCfg?.maxTurns,
-        maxBudgetUsd: agentCfg?.maxBudgetUsd,
+        ...(agentCfg ? { maxBudgetUsd: agentCfg.maxBudgetUsd } : {}),
         settingSources: agentCfg?.settingSources,
         toolAllow: agentCfg?.toolAllow,
         toolDeny: agentCfg?.toolDeny,