The invention belongs to the field of lathes, and particularly relates to a clearance adjustment device for a numerically-controlled plane milling and boring machine. The device is characterized in that a carriage (5) is evenly provided with the clearance adjustment device; the clearance adjustment device consists of a spring gland (4a), a spring (4b), a bearing block (4c), a bearing (4f), a locking nut and a locking bolt; the spring gland is connected with the carriage (5) through the locking nut and the locking bolt; the spring is arranged in the spring gland and placed at the upper end face of the bearing block; and the lower end of the bearing block is connected with the bearing which is matched with a sliding chute (1a) arranged on a cross beam. The clearance adjustment device can compensate the clearance during practical processing of the lathe in real time, effectively reduce the abrasion of a guide rail and improve the processing precision, and has good precision retaining property.