The invention discloses a prophy angle provided with a novel polishing cup and capable of clockwise and anticlockwise rotating repeatedly of a tooth polishing machine. The prophy angle comprises the polishing cup and a driving assembly, wherein the polishing cup comprises a cup body and a base; a plurality of first blades are spirally arranged in the cup body; a plurality of rhombic bulges are uniformly arranged on the outer wall of the cup body; a transmission groove is formed in the rear part of the base; a transmission curved surface is formed in the transmission groove; an assembling hole is formed in the center of the transmission curved surface; a plurality of convex parts and concave parts are arranged on the transmission curved surface, and rise and fall regularly; the driving assembly comprises a rotary main shaft; the upper end of the driving assembly is arranged in the assembling hole in a penetrating manner and is provided with a driving head part; a driving surface is formed on the driving head part, and the driving head part is meshed with the transmission curved surface, so as to realize transmission connection of the rotary main shaft and the polishing cup; when the driving surface of the driving head part is in contact with the convex parts and the concave parts of the transmission curved surface in sequence, the polishing cup can clockwise and anticlockwise rotate in sequence. The prophy angle disclosed by the invention is more stable in polishing paste control, better in polishing effect and low in heat value, can decrease the probability of damage to a dental tissue, and is low in production cost.