diff --git a/backend/app/services/backtest.py b/backend/app/services/backtest.py
index c58171f..8de8eca 100644
--- a/backend/app/services/backtest.py
+++ b/backend/app/services/backtest.py
@@ -5,6 +5,7 @@
 from __future__ import annotations
 
 import logging
+import math
 import uuid
 from dataclasses import dataclass, field
 from datetime import date, timedelta
@@ -424,10 +425,16 @@ def _config_to_dict(c: BacktestConfig) -> dict:
 
 
 def _json_safe(v):
+    # 非有限浮点 (inf / NaN) 必须先于原生标量分支拦下: Starlette 的 JSONResponse 用
+    # json.dumps(allow_nan=False) 渲染, 漏一个就是整个响应 500。pf.stats() 经
+    # pandas Series.to_dict() 出来时 numpy 标量已被装箱成原生 float (全胜时
+    # Profit Factor = inf, 零波动时 Sharpe = NaN), 两条分支都要覆盖。
+    if isinstance(v, (float, np.floating)) and not math.isfinite(float(v)):
+        return None
     if isinstance(v, (int, float, str, bool)) or v is None:
         return v
     if isinstance(v, (np.floating, np.integer)):
-        return float(v) if not np.isnan(float(v)) else None
+        return float(v)
     if hasattr(v, "isoformat"):
         return v.isoformat()
     return str(v)
diff --git a/backend/tests/test_backtest_stats_json_safe.py b/backend/tests/test_backtest_stats_json_safe.py
new file mode 100644
index 0000000..745da8c
--- /dev/null
+++ b/backend/tests/test_backtest_stats_json_safe.py
@@ -0,0 +1,84 @@
+"""信号回测统计里的 inf/NaN 必须在出接口前清成 null。
+
+Starlette 的 JSONResponse 用 json.dumps(..., allow_nan=False) 渲染, 响应体里
+只要出现一个 inf/NaN, 整个 POST /api/backtest/run 直接 500
+(ValueError: Out of range float values are not JSON compliant)。
+
+vectorbt 的 pf.stats() 常态产出这类值: 全部交易都盈利时 Profit Factor = inf,
+零波动/无交易时 Sharpe 等为 NaN; pandas 的 Series.to_dict() 会把 numpy 标量
+装箱成原生 float, 所以 _json_safe 的 (int, float, str, bool) 分支会原样放行。
+"""
+from __future__ import annotations
+
+import json
+from datetime import date
+
+import numpy as np
+import pytest
+
+from app.services.backtest import _config_to_dict, _json_safe
+
+
+def _render_like_starlette(payload) -> str:
+    """与 starlette.responses.JSONResponse.render 同参数。"""
+    return json.dumps(payload, ensure_ascii=False, allow_nan=False, separators=(",", ":"))
+
+
+@pytest.mark.parametrize(
+    "value",
+    [
+        float("inf"),          # Profit Factor: 没有亏损单
+        float("-inf"),
+        float("nan"),          # Sharpe / Sortino: 零波动
+        np.float64("inf"),
+        np.float64("nan"),
+    ],
+)
+def test_non_finite_values_become_null(value):
+    assert _json_safe(value) is None
+
+
+def test_stats_dict_survives_starlette_json_render():
+    """pf.stats() 形态的统计字典清洗后可被 allow_nan=False 渲染。"""
+    stats_dict = {
+        "Total Return [%]": 12.5,
+        "Profit Factor": float("inf"),   # 全胜 → gross_loss = 0
+        "Sharpe Ratio": float("nan"),
+        "Max Drawdown [%]": np.float64(3.25),
+        "Start": date(2026, 1, 2),
+    }
+
+    cleaned = {k: _json_safe(v) for k, v in stats_dict.items()}
+    rendered = json.loads(_render_like_starlette(cleaned))
+
+    assert rendered["Profit Factor"] is None
+    assert rendered["Sharpe Ratio"] is None
+    assert rendered["Total Return [%]"] == 12.5
+    assert rendered["Max Drawdown [%]"] == 3.25
+    assert rendered["Start"] == "2026-01-02"
+
+
+def test_finite_and_non_float_values_pass_through():
+    """回归保护: 有限数值/字符串/bool/None/日期的既有行为不变。"""
+    assert _json_safe(1.5) == 1.5
+    assert _json_safe(np.float64(2.5)) == 2.5
+    assert _json_safe(3) == 3
+    assert _json_safe(np.int64(4)) == 4
+    assert _json_safe("abc") == "abc"
+    assert _json_safe(True) is True
+    assert _json_safe(None) is None
+    assert _json_safe(date(2026, 1, 2)) == "2026-01-02"
+
+
+def test_config_payload_is_json_renderable():
+    """/api/backtest/run 的 config 段本身无非法浮点 (对照组)。"""
+    from app.services.backtest import BacktestConfig
+
+    cfg = BacktestConfig(
+        symbols=["600000.SH"],
+        start=date(2026, 1, 2),
+        end=date(2026, 2, 2),
+        entries=["signal_ma_golden_5_20"],
+        exits=[],
+    )
+    _render_like_starlette(_config_to_dict(cfg))