rotating the bones causes the model to squish

[Handsome Mug]

any idea how and why the model squish when i rotate the specific bone

[Mailer]

Are you doing it in pose mode? Try selecting the bone, then select the mesh. Then switch over to Weight Paint mode and make sure the paint isn't smothered all over the model from that bone.
I find that distant mesh, that's painted on a distant bone can get unwanted deformations and other things if also tied to a different bone that is closer.

[Pte Jack]

Yep, it sound like you have multiple bones weight painted to the mesh that is squishing where it shouldn't.

[Handsome Mug]

ill try thanks guys