The utility model discloses an anti -theft lock, lock including protection box, baffle, bayonet lock, connecting piece, I shape lever principle board, guide rail, protection box spring key hole, bolt connection spare, extension spring, baffle track and main part and insert the rod socket, its characterized in that, the welding of anti -theft lock main part U type lock is equipped with protection box spring key hole in the middle of the protection box in the protection box, be equipped with the guide rail between protection box key hole and main part lockhole, I shape lever principle board and baffle are connected to the connecting piece, and the baffle bottom is equipped with the baffle track before the main part lock lockhole, and I shape lever principle board is connected to extension spring one end, and the extension spring other end welds in the protection box, the main part lockhole is blocked to baffle in the protection box and bayonet lock one end, and the other end blocks the main part lock, and to insert this kind of anti -theft lock of rod socket be the lockhole of master lock in the middle of the people of outside can't see, and the lockhole receives the protection, and outside normal lock, the lock on both sides blocks U type lock 1/2nd again, and protection U type is locked and is not pried open.