The invention relates to a closed type anti-theft lock, which effectively solves the problems that the traditional anti-theft lock has the defects of complicated structure, high cost and poor anti-theft effect. The closed type anti-theft lock is structurally characterized in that a lock cylinder is arranged in a lock sleeve and provided with a key slot at the front end; a rear spring sheet is arranged in a lock-cylinder rear spring sheet hole on the lock cylinder, a lower ball is arranged in a lower ball hole behind the lock-cylinder rear spring sheet hole, an eccentric blind hole is arrangedon the lock cylinder on the outer side of the lower ball hole, lock-cylinder front spring sheet holes are arranged on two side walls of the lock cylinder in front of the lock-cylinder rear spring sheet, and front spring sheets are arranged in the lock-cylinder front spring sheet holes; the front and the rear spring sheets are mutually controlled and engaged together; the lock sleeve is respectively provided with a lock-sleeve rear spring sheet hole and a lock-sleeve front spring sheet hole; the rear ball in the lock-sleeve rear spring sheet hole is provided with a first spring and the front ball in the lock-sleeve front spring sheet hole is provided with a second spring; an upper ball hole is arranged behind the lock-sleeve rear spring sheet hole and a third spring is fixed on the upper ball in the upper ball hole; and the key slot is provided with a key matched with the lock cylinder to form a closed type anti-theft structure. The closed type anti-theft lock provided by the inventionhas the advantages of simple manufacturing process, unique structure, firmness and durability and good anti-theft effect.