I’ve got a third person game there’s a player in it with character controller assigned to it. So my problem is that player walks through the imported game objects with mesh colliders.
What is wrong with that? How to fight with that?
P.S.
In some places of the object it can’t walk through
What kind of models are we talkin about? If you don’t weld your models (snap vertices together and weld) collision can fail(im going off my ventures with other game engines) i have never had that problem with unity,but something to consider. Sometimes if things are moving too fast it will break through as well. Have u tried an additional collider to your character?
Just some trouble shooting 
yes i’ve added additional colliders but still result is the same… The speed of the player is slow.
Have you tried adjusting the SkinWidth on the CharacterController?