diff --git a/BMM/BMM_Theory/bmm_theory/branches/merge_batch.py b/BMM/BMM_Theory/bmm_theory/branches/merge_batch.py
index 43038d2..f7142de 100644
--- a/BMM/BMM_Theory/bmm_theory/branches/merge_batch.py
+++ b/BMM/BMM_Theory/bmm_theory/branches/merge_batch.py
@@ -7,6 +7,8 @@
 核心思想: 合并 b0 个 batch 的 A'[b0*M,K] @ B'[K,b0*N] 为单次 DMA 搬入,
 减少 GM->L1 搬移命令数 (省 b0 倍 T_cmd); 交叉项被算出但丢弃 (冗余比例 (b0-1)/b0),
 进入条件 5 保证 case 为访存 Bound, 冗余算力被搬移时延掩盖.
+T_cmd=0 时 (无命令固定开销) 合并失去唯一收益来源, 分界仲裁直接判 MergeBatch
+不胜出 (beats_iterbatch 对 T_cmd<=0 做 +inf 处理, 见函数内说明).
 """
 
 from __future__ import annotations
@@ -222,6 +224,8 @@ class MergeBatchBranch(Branch):
 
         MergeBatch 最优  ⟺  K截断 (k_L1=K) 且 b_core > b0*(T_comp+T_write)/T_cmd
         L1 绑定情形 MergeBatch 恒劣于 IterBatch (搬移次数相同, 只放大 drain).
+        T_cmd=0 时阈值趋于无穷: 合并的唯一收益 (省 DMA 命令开销) 消失,
+        只剩 drain 放大与冗余计算, MergeBatch 无胜出通道 (见 evaluate 对拍也一致).
         """
         s = self.spec
         m, n, k = case.m, case.n, case.k
@@ -237,12 +241,21 @@ class MergeBatchBranch(Branch):
         b0 = plan.merge_b0
         t_comp = 2.0 * m * n * min(k_l1_iter, k) / s.q16
         t_write = m * n * out_b / s.bw_pc
+        drain_pen = (b0 - 1) * (t_comp + t_write)
+
+        if s.t_cmd <= 0:
+            # T_cmd=0: 阈值 b0*(T_comp+T_write)/T_cmd -> +inf, 不可除零, 直接判负
+            detail = (f"k_L1={'K(截断)' if k_truncated else f'{k_l1_iter:.0f}<K(L1绑定)'}; "
+                      f"T_cmd=0: 合并无命令开销节省 (阈值=+inf), MergeBatch 无胜出通道; "
+                      f"仅剩 drain 惩罚=(b0-1)*(T_comp+T_write)={drain_pen*1e6:.2f}us")
+            return False, detail
+
         threshold = b0 * (t_comp + t_write) / s.t_cmd
 
         win = k_truncated and (b_core > threshold)
         detail = (f"k_L1={'K(截断)' if k_truncated else f'{k_l1_iter:.0f}<K(L1绑定)'}; "
                   f"b_core={b_core} vs 阈值 b0*(T_comp+T_write)/T_cmd={threshold:.1f}; "
-                  f"drain惩罚=(b0-1)*(T_comp+T_write)={((b0-1)*(t_comp+t_write))*1e6:.2f}us, "
+                  f"drain惩罚=(b0-1)*(T_comp+T_write)={drain_pen*1e6:.2f}us, "
                   f"搬移节省=b_core*(1-1/b0)*T_cmd={b_core*(1-1/b0)*s.t_cmd*1e6:.2f}us")
         return win, detail
 
diff --git a/BMM/BMM_Theory/tests/test_branches.py b/BMM/BMM_Theory/tests/test_branches.py
index 2d9c0eb..5c1cfd1 100644
--- a/BMM/BMM_Theory/tests/test_branches.py
+++ b/BMM/BMM_Theory/tests/test_branches.py
@@ -369,5 +369,55 @@ class TestTransposeModeling(unittest.TestCase):
             self.assertFalse(c4.passed, f"A 不转置时 K=8 应报 dValue 违规: {c4.detail}")
 
 
+class TestZeroCmdHandling(unittest.TestCase):
+    """T_cmd=0 (无 DMA 命令固定开销) 时整链路不得除零/崩溃, 建模语义正确."""
+
+    def test_beats_iterbatch_no_division_error(self):
+        # T_cmd=0 时阈值 b0*(T_comp+T_write)/T_cmd -> +inf, MergeBatch 必须判不胜出
+        from bmm_theory.hardware import NpuSpec
+        from bmm_theory.branches.merge_batch import MergeBatchBranch
+        spec0 = NpuSpec(t_cmd_ns=0.0)
+        mb = MergeBatchBranch(spec0)
+        for b, m, n, k in [(2048, 32, 32, 256), (128, 64, 64, 512), (256, 128, 128, 4096)]:
+            win, detail = mb.beats_iterbatch(mkcase(b, m, n, k))
+            self.assertFalse(win, f"T_cmd=0 时 MergeBatch 不应胜出: {detail}")
+            self.assertIn("T_cmd=0", detail)
+
+    def test_route_with_zero_cmd_no_crash(self):
+        # 整条路由链 (含仲裁) 在 T_cmd=0 下无异常, 时延有限且 MergeBatch 让位 IterBatch
+        from bmm_theory.hardware import NpuSpec
+        router = BranchRouter(NpuSpec(t_cmd_ns=0.0))
+        r = router.route(mkcase(2048, 32, 32, 256))  # 原 MergeBatch 典型胜场形状
+        self.assertEqual(r["branch"], "IterBatch")   # 命令节省消失 -> 无合并价值
+        self.assertIsNotNone(r["timing"])
+        shapes = [(128, 64, 64, 512), (64, 64, 64, 8192), (512, 128, 128, 128),
+                  (128, 128, 128, 1024), (32, 4096, 4096, 4096)]
+        for b, m, n, k in shapes:
+            rr = router.route(mkcase(b, m, n, k))
+            t = rr["timing"]
+            self.assertIsNotNone(t, f"{b},{m},{n},{k} 应有 timing")
+            self.assertGreater(t.t_total, 0.0)
+            self.assertEqual(t.t_total, t.t_total)  # 非 NaN
+
+    def test_zero_cmd_random_smoke(self):
+        # 随机小样本冒烟: 无异常/无 NaN
+        import random
+        from bmm_theory.hardware import NpuSpec
+        router = BranchRouter(NpuSpec(t_cmd_ns=0.0))
+        rng = random.Random(9)
+        for _ in range(300):
+            b = rng.choice([2, 4, 8, 16, 32, 64, 128, 256, 512, 1024, 2048])
+            m = rng.choice([8, 16, 32, 64, 128, 256, 512, 1024, 4096])
+            n = rng.choice([8, 16, 32, 64, 128, 256, 512, 1024, 4096])
+            k = rng.choice([16, 32, 64, 128, 256, 512, 1024, 4096, 16384])
+            c = BmmCase(case_id="z", batch_a=b, batch_b=b, m=m, n=n, k=k)
+            rr = router.route(c)
+            self.assertIsNotNone(rr["plan"])
+            t = rr["timing"]
+            self.assertIsNotNone(t)
+            self.assertGreater(t.t_total, 0.0)
+            self.assertEqual(t.t_total, t.t_total)
+
+
 if __name__ == "__main__":
     unittest.main()