some times. I need to manufacture a finer terrain in 3ds max,how to import to unity3d like unity3d terrain?
You probably have to get height map out of max IF you want to use the Unity terrain object. You can make a height map by making a plane under your terrain and baking height/bump to it, if I remember right, haven’t used max for years now.
Not 100% sure, but its pretty much likely you can’t convert the mesh to unity terrain, but if you do some magic tricks by piecing up the terrain and then using those terrains with some clever manual LODding… You’ll get good results (performance and looks wise) 
Oh, and you can change the resolution of the Unity terrain if it feels like its too rough