Abstract: The geometric properties of the screw rotor directly determine the working performance of the twin-screw vacuum pump. In order to solve the problem of long spatial contact curve and large leakage triangle area of the existing screw rotors, a meshing model of the sinusoidal helix, as well as the elliptic arc and their conjugate curves, is established in this study. A new screw rotor composed of a sinusoidal helix-elliptic arc is designed, and its profile equation is derived. The existing rotors and the new rotors are compared by means of geometric analysis of screw rotors and numerical simulation of their working process. The results show that the length of the spatial contact curve of the proposed screw rotor is shortened by 2.54%, and the leakage triangle area is reduced by 27.77%; the leakage depth of the tooth tip is significantly smaller than that of the existing rotor, which has better sealing performance and effectively improves the function of the twin-screw vacuum pump. It has important theoretical significance and practical engineering value for improving the leakage of the twin screw vacuum pump.