diff --git a/dpdata/lmdb/format.py b/dpdata/lmdb/format.py
index 9b518be6..2e7ae3c4 100644
--- a/dpdata/lmdb/format.py
+++ b/dpdata/lmdb/format.py
@@ -2,15 +2,10 @@
 
 import os
 
-import lmdb
-import msgpack
-import msgpack_numpy as m
 import numpy as np
 
 from dpdata.format import Format
 
-m.patch()
-
 
 class LMDBError(Exception):
     """Base class for LMDB errors."""
@@ -63,6 +58,11 @@ class LMDBFormat(Format):
     >>> loaded_multi_systems = dpdata.MultiSystems.from_file("my_multi_system_db.lmdb", fmt="lmdb")
     """
 
+    def __init__(self, *args, **kwargs) -> None:
+        import msgpack_numpy as m
+
+        m.patch()
+
     def to_multi_systems(
         self, formulas, directory, map_size=1000000000, frame_idx_fmt="012d", **kwargs
     ):
@@ -86,6 +86,9 @@ def to_multi_systems(
         tuple
             (self, formula) to be used by to_system
         """
+        import lmdb
+        import msgpack
+
         self._frame_idx_fmt = frame_idx_fmt
         self._global_frame_idx = 0
         self._system_info = []
@@ -105,6 +108,8 @@ def to_multi_systems(
                 self._txn = None
 
     def _dump_to_txn(self, data, txn, formula, dtypes):
+        import msgpack
+
         from dpdata.data_type import Axis
 
         nframes = data["coords"].shape[0]
@@ -209,6 +214,9 @@ def from_multi_systems(self, file_name, map_size=1000000000, **kwargs):
         dict
             data dictionary for each system
         """
+        import lmdb
+        import msgpack
+
         from dpdata.data_type import Axis, DataType
         from dpdata.system import LabeledSystem, System