I have many “area” model, and i want add some of them into my project instead of terrain. But when i let my character run on these model, my char was droped into the hell.
I know the problem is my area model dont have gravity like Terrain.
So are there anyway to convert normal model to Terrain ? Or do i need to modify the model to fit with Unity ? 
Thank you very much ^^
Add a Mesh Collider.
It won’t make it a ‘terrain’, but it will allow your characters to walk on it.
You have a very useful script made by the community : http://www.unifycommunity.com/wiki/index.php?title=Object2Terrain
you have to modify the mesh to fit.
A mesh can never become a terrain, you could only use some modelling software to generate a heightmap from the terrain to use that then to get the form of the terrain back but that assumes that the original you create the heightmap from was a “correct terrain” not something with overhangs etc