A supplementing reinforcing tool for a horizontal well sleeve comprises an adjusting pipe, an upper expanding head, a lower expanding head, an upper sealing pipe, a lower sealing pipe, a center rod, a supplementing pipe, a lower pipe, a valve ball, a shear pin sleeve, a shear pin, a ball seat, a steel ball, a ball sleeve, a valving lock claw, a baffling sleeve, a lower plug and a lock ring. The adjusting pipe is sequentially connected with the upper expanding head, the upper sealing pipe, the supplementing pipe, the lower sealing pipe and the lower expanding head. The upper portion of the ball sleeve is connected with the shear pin sleeve and the ball seat, and the lower portion of the ball sleeve is connected with the lower plug and the lock ring. The valving lock claw is respectively connected with the lower plug, the lower expanding head and the shear pin sleeve, and the lower pipe is respectively connected with the center rod and the shear pin sleeve. The supplementing reinforcing tool for the horizontal well sleeve has the advantages of meeting using requirements of a horizontal well section, being high in sealing strength, good in reinforcing stability, long in service life and convenient to construct and the like, and is widely applied to a supplementing process of the oil production well sleeve.