The invention relates to a mechanism digital lock. A variable-pitch locking dog of a mechanical digital lock consists of a main locking dog and an auxiliary locking dog, wherein the main locking dog is a lock clamping end, the main locking dog and the auxiliary locking dog are connected in a sliding way by a sliding rail and a track slot, the lock clamping end is provided with a return spring hole parallel to the sliding rail, two side surfaces of the return spring hole are provided with lock clamping plate driving pins, the auxiliary locking dog is provided with a spring stabilizing penetrating pin corresponding to the return spring hole of the main locking dog, a spring is arranged on the spring stabilizing penetrating pin and is assembled with the return spring hole, and the main locking dog and the auxiliary locking dog are provided with relative travel limiting devices. The variable-pitch locking dog has a simple structure, and adopts a two-body structure; the main locking dog and the auxiliary locking dog are sheathed together coaxially in a sliding way, and can slide relatively to realize a variable-pitch integral structure; and variable-pitch control on the main locking dog and the auxiliary locking dog can be conducted freely by a handle indoors and outdoors, therefore, the mechanical digital lock can be freely controlled to be opened and closed from the inner side and the outer side, and can be used on a door body such as an antitheft door and the like.