Thanks for your patient!
Have the post above, but I don’t think the problem is about my skeletal mesh. The arms comes from starter content and have “SK_Mannequin_Arms_PhysicsAsset” with it, so it’s physics works well actually.
And I don’t think character’s capsule collision matters here. I just don’t need character itself’s collision and just only demonstrate the arms skeletal mesh collision to show you the problems.