This is a super convenient plug-in. It directly turns the max exported terrain into a U3d terrain.
1, unzip the attachment and put it into the project resource file and the directory.
2, import the terrain objects from 3D Max or Maya into the unity3d resource folder;
3, click on the Terrain--->Create Terrain in the toolbar menu to create a terrain;
4, drag the imported terrain from the Unity3D Project panel to the Hierarchy panel. In the Hierarchy panel, select the model object that you just imported. Remember to select the object with mesh. Then select the Terrain--->3DObject to Terrain. in the toolbar menu, then you can see the modified terrain you imported yourself.