The invention provides a belt pulley. The belt pulley is in the basic shape of a circular ring, a flexible movable block with an annular opening is arranged on the outer diameter of the circular ring, a clutch supporting surface is arranged at one side of the circular ring, a bearing hole is formed in the middle of the clutch supporting surface, fan-shaped grooves are formed in the outer wall of the clutch supporting surface, and convex lugs are arranged in grooves which are arranged at intervals; a pressing disc limiting groove is formed in the inner wall of the circular ring of the inner side of the clutch supporting surface, grooves are formed in the middles of convex portions of the pressing disc limiting groove, installation holes are formed in the two sides of each convex portion, lever separation holes are formed in the portions, corresponding to the grooves, of the clutch supporting surface, and clutch plate installation platforms are arranged at the positions, corresponding to the installation holes, of the inner diameter of the pressing disc limiting groove. According to the belt pulley, a direct casting shaping process method is adopted, a complete groove-shaped cavity is obtained by adopting a precoated sand shell molding process, a groove shape is directly cast, a process method which is free of cutting or needs an extremely little amount of cutting is obtained, and method is low in cost, simple, easy to operate and suitable for being used by most enterprises.