The invention discloses a safety anti-theft lock capable of preventing a precision mechanical twist lock head from being damaged. When a key is not inserted, a positioning ball is positioned between aradial slot and a limiting slot; under the limiting action of the positioning ball, a rotor cannot rotate; when the key is inserted into an outer lock cylinder, the key is inserted to drive an outerrotary block to move inwards, so that an outer combined structure between the outer rotary block and the rotor is combined; the outer rotary block which moves inwards drives a rotary core of the rotorto move inwards, and the positioning ball is separated from a limiting slot, so that the rotor can be driven to rotate to unlock; when a lock body receives exogenic action and the lock body is separated from a pull-apart slot, the outer rotary block moves towards the outer side and is separated from a small-diameter section under action of an outer return spring while a steel ball drops to the slot bottom of a radial vertical slot, the small-diameter section is sealed, and the rotor cannot rotate to unlock as a result of the limiting effect, on the rotor, of the positioning ball, and therefore, the locking technical purpose is achieved. Summing up from the above, an unlocking mechanism is adopted, so that safety protective performance can be effectively improved, and reliability is better.