diff --git a/deepmd/dpmodel/utils/batch.py b/deepmd/dpmodel/utils/batch.py
index d5657fc76d..340225c060 100644
--- a/deepmd/dpmodel/utils/batch.py
+++ b/deepmd/dpmodel/utils/batch.py
@@ -37,6 +37,8 @@ def normalize_batch(batch: dict[str, Any]) -> dict[str, Any]:
     * ``"type"`` is renamed to ``"atype"`` (int64).
     * ``"natoms_vec"`` (1-D) is tiled to 2-D ``[nframes, 2+ntypes]``
       and stored as ``"natoms"``.
+    * Non-periodic ``default_mesh`` encodings set the canonical model input
+      ``box`` to ``None``.
     * ``find_*`` flags are converted to ``np.bool_``.
     * Metadata keys (``default_mesh``, ``sid``, ``fid``) are dropped.
 
@@ -56,6 +58,11 @@ def normalize_batch(batch: dict[str, Any]) -> dict[str, Any]:
         Normalized batch dict (new dict; the input is not mutated).
     """
     out: dict[str, Any] = {}
+    default_mesh = batch.get("default_mesh")
+    mesh_says_nonperiodic = default_mesh is not None and np.size(default_mesh) in (
+        0,
+        1,
+    )
 
     for key, val in batch.items():
         if key in _DROP_KEYS:
@@ -74,6 +81,9 @@ def normalize_batch(batch: dict[str, Any]) -> dict[str, Any]:
         else:
             out[key] = val
 
+    if mesh_says_nonperiodic and "box" in out:
+        out["box"] = None
+
     if out.get("charge_spin") is not None and bool(out.get("find_charge_spin", True)):
         validate_charge_states(out["charge_spin"])
 
diff --git a/source/tests/common/test_batch_nopbc.py b/source/tests/common/test_batch_nopbc.py
new file mode 100644
index 0000000000..730a3f502a
--- /dev/null
+++ b/source/tests/common/test_batch_nopbc.py
@@ -0,0 +1,107 @@
+# SPDX-License-Identifier: LGPL-3.0-or-later
+"""Preserve periodic-boundary semantics across batch normalization."""
+
+import tempfile
+import unittest
+from pathlib import (
+    Path,
+)
+
+import numpy as np
+
+from deepmd.dpmodel.utils.batch import (
+    normalize_batch,
+    split_batch,
+)
+from deepmd.utils.data_system import (
+    DeepmdDataSystem,
+)
+
+
+class TestNormalizeBatchPBC(unittest.TestCase):
+    """Translate the legacy mesh encoding before dropping its metadata."""
+
+    @staticmethod
+    def _batch(default_mesh_size: int, box: np.ndarray) -> dict:
+        return {
+            "coord": np.zeros((1, 2, 3)),
+            "type": np.zeros((1, 2), dtype=np.int32),
+            "box": box,
+            "default_mesh": np.zeros(default_mesh_size, dtype=np.int32),
+        }
+
+    def test_nonperiodic_box_is_none(self) -> None:
+        for mesh_size in (0, 1):
+            with self.subTest(mesh_size=mesh_size):
+                box = np.eye(3).reshape(1, 9)
+                batch = self._batch(mesh_size, box)
+
+                normalized = normalize_batch(batch)
+
+                self.assertIsNone(normalized["box"])
+                self.assertNotIn("default_mesh", normalized)
+                self.assertIs(batch["box"], box)
+
+    def test_periodic_box_is_preserved(self) -> None:
+        for mesh_size in (6, 7):
+            with self.subTest(mesh_size=mesh_size):
+                box = np.eye(3).reshape(1, 9)
+
+                normalized = normalize_batch(self._batch(mesh_size, box))
+
+                self.assertIs(normalized["box"], box)
+
+    def test_missing_default_mesh_preserves_box(self) -> None:
+        box = np.eye(3).reshape(1, 9)
+        batch = self._batch(0, box)
+        del batch["default_mesh"]
+
+        normalized = normalize_batch(batch)
+
+        self.assertIs(normalized["box"], box)
+
+    def test_nonperiodic_mesh_without_box_does_not_add_box(self) -> None:
+        batch = self._batch(0, np.eye(3).reshape(1, 9))
+        del batch["box"]
+
+        normalized = normalize_batch(batch)
+
+        self.assertNotIn("box", normalized)
+
+
+class TestDeepmdDataSystemNopbc(unittest.TestCase):
+    """A valid nopbc NPY system must reach the model without a box."""
+
+    def test_zero_box_placeholder_is_removed(self) -> None:
+        with tempfile.TemporaryDirectory() as tmpdir:
+            system = Path(tmpdir)
+            set_dir = system / "set.000"
+            set_dir.mkdir()
+            (system / "type.raw").write_text("0 0\n")
+            (system / "type_map.raw").write_text("H\n")
+            (system / "nopbc").touch()
+            np.save(
+                set_dir / "coord.npy",
+                np.array([[0.0, 0.0, 0.0, 0.74, 0.0, 0.0]]),
+            )
+
+            data_system = DeepmdDataSystem(
+                [str(system)],
+                batch_size=1,
+                test_size=1,
+                rcut=6.0,
+                type_map=["H"],
+                trn_all_set=True,
+                shuffle_test=False,
+            )
+            raw = data_system.get_batch()
+            inputs, _ = split_batch(normalize_batch(raw))
+
+            self.assertFalse(data_system.data_systems[0].pbc)
+            self.assertEqual(raw["default_mesh"].size, 0)
+            self.assertTrue(np.allclose(raw["box"], 0.0))
+            self.assertIsNone(inputs["box"])
+
+
+if __name__ == "__main__":
+    unittest.main()