diff --git a/backend/app/services/analytics_service.py b/backend/app/services/analytics_service.py
index dbcb53a..b35480b 100644
--- a/backend/app/services/analytics_service.py
+++ b/backend/app/services/analytics_service.py
@@ -342,25 +342,10 @@ async def get_flow_compare(
     if not product_rows:
         return FlowResponse(devices=[], series=[])
 
-    devices = [
-        FlowDevice(
-            product_sn=r[1], external_serial=r[2],
-            material_name=r[3] or "", spec_model=r[4] or "",
-            lead_time=0.0,
-            started_at="",
-        )
-        for r in product_rows
-    ]
-    # 显式传入身份证时按输入顺序排列
-    if product_sns:
-        order = {sn: i for i, sn in enumerate(product_sns)}
-        devices.sort(key=lambda d: order.get(d.product_sn, len(order)))
-
     id_to_sn = {r[0]: r[1] for r in product_rows}
-    sn_to_index = {d.product_sn: i for i, d in enumerate(devices)}
     product_ids = [r[0] for r in product_rows]
 
-    # ── 这些设备的全部任务（含工序名，用于区间图） ──
+    # ── 候选设备的全部任务（含工序名，用于区间图） ──
     task_rows = (await db.execute(
         select(
             Task.product_id, Task.assignee_id, Task.task_name,
@@ -374,25 +359,57 @@ async def get_flow_compare(
         )
     )).all()
 
-    # ── 解析为区间记录，并计算每台设备的 T0（最早）与 max_end（最晚） ──
+    # ── 设备级时间筛选 ──
+    # 语义：时间筛选 = "在该时间有活动的设备"，而非"把任务切片只保留该时间"。
+    # 设备一旦入选，其任务必须完整返回（完整生命周期），绝不因设备在筛选中无新动作
+    # 而把它的历史任务清空。
+    if since is not None or until is not None:
+        active_pids: set = set()
+        for row in task_rows:
+            pid = row[0]
+            start = _to_bj(row[3] or row[4])
+            end = _to_bj(row[5]) if row[5] else now
+            if start is None:
+                continue
+            if since is not None and end < since:
+                continue
+            if until is not None and start > until:
+                continue
+            active_pids.add(pid)
+        product_rows = [r for r in product_rows if r[0] in active_pids]
+    if not product_rows:
+        return FlowResponse(devices=[], series=[])
+
+    # 显式传入身份证时按输入顺序排列
+    if product_sns:
+        order = {sn: i for i, sn in enumerate(product_sns)}
+        product_rows.sort(key=lambda r: order.get(r[1], len(order)))
+    devices = [
+        FlowDevice(
+            product_sn=r[1], external_serial=r[2],
+            material_name=r[3] or "", spec_model=r[4] or "",
+            lead_time=0.0,
+            started_at="",
+        )
+        for r in product_rows
+    ]
+    sn_to_index = {d.product_sn: i for i, d in enumerate(devices)}
+    kept_ids = {r[0] for r in product_rows}
+
+    # ── 解析为区间记录（完整生命周期，不再按时间切片） ──
     intervals: list[dict] = []
     t0_by_device: dict[int, datetime] = {}
     max_end_by_device: dict[int, datetime] = {}
     for row in task_rows:
         pid, assignee_id, task_name, received_at, created_at, completed_at, task_type = row
-        sn = id_to_sn.get(pid)
-        if sn is None or sn not in sn_to_index:
+        if pid not in kept_ids:
             continue
+        sn = id_to_sn[pid]
         idx = sn_to_index[sn]
         start = _to_bj(received_at or created_at)
         end = _to_bj(completed_at) if completed_at else now
         if start is None:
             continue
-        # 时间筛选：任务区间与 [since, until] 有交集
-        if since is not None and end is not None and end < since:
-            continue
-        if until is not None and start is not None and start > until:
-            continue
         is_main = 0 if task_type == "SPAWN" else 1
         intervals.append({
             "idx": idx,