Abstract: The rotors for screw compressor include a male rotor and a female rotor. The cross-sectional profile of the male rotor is composed of four circular curves, curves generated by two circular curves and a circular curve that are sequentially connected with each other. The cross-sectional profile of the female rotor is composed of eight curves generated by four circular curves, a curve generated by a point and three curves. They arc sequentially connected with each other. Not only the continuity of each curve is good, but also the continuity of the connecting section between the curves is excellent. So, the operation of the rotors can be kept smooth and the compression efficiency is enhanced.