The invention belongs to the technical field of belt transmission, and in particular relates to a transmission mechanism for a high-speed belt, which includes a driving shaft, a driving wheel, a first output shaft, a driven wheel, a belt, a stretching mechanism, a lower pulley, an upper pulley, a differential device, first bevel tooth combination, centrifugal wheel, driving hollow wheel, centrifugal block, centrifugal block spring, etc., when the belt is in high-speed transmission, the upper pulley and the lower pulley make the differential work at different speeds, then the differential The device drives the stretching mechanism to lift the belt through the combination of bevel teeth, centrifugal wheel and driving hollow wheel, so that the belt is in a tensioned state and realizes the high-speed transmission of the belt. The invention solves the problem of the belt slipping phenomenon in the high-speed transmission of the traditional belt mechanism, and finally enables the belt transmission mechanism to realize high-speed transmission. The structure is simple and compact, and has good practical effect.