diff --git a/backend/app/services/rps_rotation.py b/backend/app/services/rps_rotation.py
index bfeb8da..fe88b63 100644
--- a/backend/app/services/rps_rotation.py
+++ b/backend/app/services/rps_rotation.py
@@ -35,12 +35,16 @@ logger = logging.getLogger(__name__)
 _CACHE_TTL = 120.0
 _cache: dict[str, dict] = {}
 _cache_ts: dict[str, float] = {}
+# 该条目实际覆盖的天数: enriched 只读 days 换算出的日历窗口, 缓存的"全量"因此
+# 以写入时的 days 为上限, 请求更长窗口时不能复用 (见 build_rps_rotation)。
+_cache_days: dict[str, int] = {}
 
 
 def invalidate_cache() -> None:
     """清空轮动矩阵结果缓存(数据管道完成后调用, 避免返回旧数据)。"""
     _cache.clear()
     _cache_ts.clear()
+    _cache_days.clear()
 
 
 def _latest_enriched_date(repo) -> date | None:
@@ -138,7 +142,11 @@ def build_rps_rotation(repo, days: int = 12, kind: str = "concept", level: int |
     cache_key = f"{kind}|{level}|{latest.isoformat()}"
     now = time.time()
     cached = _cache.get(cache_key)
-    if cached and (now - _cache_ts.get(cache_key, 0)) < _CACHE_TTL:
+    if (
+        cached
+        and _cache_days.get(cache_key, 0) >= days
+        and (now - _cache_ts.get(cache_key, 0)) < _CACHE_TTL
+    ):
         return _slice_cached(cached, days)
 
     # 1. 维度映射(symbol → 维度成员), 已按 kind 缓存为 (map_df, count) 元组 (#186)。
@@ -201,9 +209,10 @@ def build_rps_rotation(repo, days: int = 12, kind: str = "concept", level: int |
         "concept_count": member_count,
     }
 
-    # 写缓存(存全量, 按需 slice)
+    # 写缓存(存本次窗口的全量, 按需 slice; 覆盖天数一并记下)
     _cache[cache_key] = full
     _cache_ts[cache_key] = now
+    _cache_days[cache_key] = days
 
     return _slice_cached(full, days)
 
diff --git a/backend/tests/test_rps_rotation_days_cache.py b/backend/tests/test_rps_rotation_days_cache.py
new file mode 100644
index 0000000..007c338
--- /dev/null
+++ b/backend/tests/test_rps_rotation_days_cache.py
@@ -0,0 +1,102 @@
+"""涨幅轮动矩阵结果缓存必须按 days 区分。
+
+build_rps_rotation 只按 days 换算出的日历窗口读 enriched (days=7 只读 24 个
+自然日), 但结果缓存键是 "{kind}|{level}|{latest}" —— 不含 days。先看 7 日
+再切到 30 日, 120s TTL 内会命中那份按 7 日窗口算出来的矩阵, 前端拿到的列数
+比请求的少。
+"""
+from __future__ import annotations
+
+import types
+from datetime import date, timedelta
+
+import polars as pl
+import pytest
+
+from app.services import rps_rotation
+
+_LATEST = date(2026, 6, 30)
+_HISTORY_DAYS = 80
+_MEMBERS = ("人工智能", "芯片")
+
+
+@pytest.fixture(autouse=True)
+def _clear_caches():
+    rps_rotation.invalidate_cache()
+    rps_rotation._map_cache.clear()
+    rps_rotation._map_ts.clear()
+    yield
+    rps_rotation.invalidate_cache()
+    rps_rotation._map_cache.clear()
+    rps_rotation._map_ts.clear()
+
+
+def _history() -> pl.DataFrame:
+    """两只票在 80 个连续自然日上的 change_pct(小数制)。"""
+    rows = []
+    for offset in range(_HISTORY_DAYS):
+        day = _LATEST - timedelta(days=offset)
+        rows.append({"symbol": "S1.SH", "date": day, "change_pct": 0.01})
+        rows.append({"symbol": "S2.SH", "date": day, "change_pct": -0.01})
+    return pl.DataFrame(rows)
+
+
+def _fake_repo() -> types.SimpleNamespace:
+    history = _history()
+
+    def get_enriched_range(start, end, columns=None):
+        df = history.filter((pl.col("date") >= start) & (pl.col("date") <= end))
+        return df.select(columns) if columns else df
+
+    return types.SimpleNamespace(
+        _enriched_history_cache=history,
+        get_enriched_range=get_enriched_range,
+        store=types.SimpleNamespace(data_dir=None),
+    )
+
+
+@pytest.fixture
+def repo(monkeypatch) -> types.SimpleNamespace:
+    map_df = pl.DataFrame(
+        {"_sym_up": ["S1.SH", "S2.SH"], "concept": list(_MEMBERS)},
+        schema={"_sym_up": pl.Utf8, "concept": pl.Utf8},
+    )
+    monkeypatch.setattr(
+        rps_rotation, "_load_concept_map_df", lambda _repo, kind: (map_df, len(_MEMBERS))
+    )
+    return _fake_repo()
+
+
+def test_widening_days_after_a_narrow_request_returns_all_days(repo):
+    """先请求 7 日再请求 30 日, 第二次必须拿到 30 列。
+
+    旧实现: 缓存键不含 days, 第二次命中第一次那份只有 25 列的矩阵。
+    """
+    narrow = rps_rotation.build_rps_rotation(repo, days=7)
+    assert len(narrow["dates"]) == 7
+
+    wide = rps_rotation.build_rps_rotation(repo, days=30)
+    assert len(wide["dates"]) == 30
+    assert len(wide["columns"]) == 30
+
+
+def test_narrowing_days_after_a_wide_request_still_slices(repo):
+    """反方向仍要按请求截断 (宽窗缓存可以复用, 但只返回请求的天数)。"""
+    wide = rps_rotation.build_rps_rotation(repo, days=30)
+    assert len(wide["dates"]) == 30
+
+    narrow = rps_rotation.build_rps_rotation(repo, days=7)
+    assert len(narrow["dates"]) == 7
+    assert narrow["dates"] == wide["dates"][:7]
+
+
+def test_same_days_request_hits_cache(repo, monkeypatch):
+    """同一 days 的重复请求仍走缓存, 不重新读 enriched。"""
+    rps_rotation.build_rps_rotation(repo, days=12)
+
+    def _boom(*args, **kwargs):
+        raise AssertionError("缓存未命中: 又读了一次 enriched")
+
+    monkeypatch.setattr(repo, "get_enriched_range", _boom)
+    again = rps_rotation.build_rps_rotation(repo, days=12)
+    assert len(again["dates"]) == 12