The utility model belongs to a tool designing technology, and relates to a clamping block for machining a chute of a cylindrical part. The clamping block consists of a clamping body, wherein the clamping body is an inclined plane hexahedron; the middle part of an upper surface of the clamping body has a positioning hole which is vertical to the upper surface and is used for placing parts; a clamping groove is formed in the middle of an inclined plane along with a lowered side of the inclined plane and is integrally connected with the part positioning hole; a tool setting groove is formed in the middle of the other side of the inclined plane and is communicated with the positioning hole; and the bottom surface of the tool setting groove is parallel to a positioning surface and the bottom surface of a part chute. The part is placed in the positioning hole in the clamping block, the clamping block is placed in a jaw vice, the positioning bottom surface of the clamping block is leveled up through a standard block and is tightly clamped by the jaw vice, the tool setting groove is aligned, and then the part can be machined. By the clamping block, the problem of difficulty in positioning and clamping of the chute in the part machining process is solved, and the chute can be quickly clamped and positioned; a cutting tool can be quickly set; the part can be quickly machined; and the machining cost is reduced, and the machining efficiency and the yield of the part are improved.