When camera get close to a mesh,near part of mesh will disappear!?

I’ve imported a .fbx file in unity and i want to move my camera around it
but when the camera gets close to a part of the model,that near part will disappear and won’t show in rendering!how can i fix it?
thanks in advance!

That’s called the “near clipping plane” – see camera manual page.

Is the problem with a camera in your game, or the camera Unity uses internally to render the scene view? If it’s your camera, it’s fairly easy to reconfigure the near clip plane.