The invention discloses a printer locking preventing device with a standby cutting-off device. The printer locking preventing device comprises a printer body, a locking preventing trimming device andthe standby cutting-off device. The locking preventing trimming device comprises a fixed blade, a movable blade seat and a movable blade. A cutting edge at the lower end of the fixed blade is formed in an inverted M shape. The standby cutting-off device comprises a cutting-off abutting block arranged on the movable blade seat in a lifting manner, an optoelectronic switch and a center processor. The cutting-off abutting block is located under a sharp corner on the rear side of the lower end of the fixed blade. The optoelectronic switch is arranged on the rear side wall of a trimming groove andpenetrates the lower middle portion of the fixed blade. The center processor is arranged on the printer body. The optoelectronic switch is connected with the center processor. The center processor controls the cutting-off abutting block to ascend and descend. According to the printer locking preventing device, when paper is clamped between the fixed blade and the movable blade, the standby cutting-off device is used for cutting off the clamped paper, and the clamped paper can be taken out conveniently. Meanwhile, blade damage caused by accidental engagement of the fixed blade and the movable blade is reduced.