big skinned mesh in editor

I create or import skinned mesh over 250000 vertices and 400000+ triangles
and have errors in UnityEditor from preview

Unity 2018.2.11f1

Its HIGHLY inadvisable to use meshes that big unless you have a really specialist reason to do it. I would use decimate in blender to simplify the mesh, and convert the extra detail into a normal map. You can do this by looking up how to create a blender normal map, one of the tutorials shows you how to use a simple and high poly model and convert the high poly into a high detail normal map.