Abstract: A novel helical straight claw rotor, based on cusp-free profile of straight rotors, was proposed for design optimization of claw vacuum pump. The original work included the structure modification of straight claw rotor with an axial spiral. The helical angle and rotor thickness were designed in such a way that the rotor pairs, rotating in opposite directions and with the same helical angle, meshes more precisely, resulting in an increased air-tightness and a decreased leakage in compression. The pumping performance of the novel helical straight and conventional straight claw rotors was evaluated in 3D numerical simulation. The simulated results show that the proposed helical straight claw rotor outperforms the conventional one because of better meshing, greater contact ratio, lower energy consumption and higher pumping efficiency. In addition, the stability, reliability and service life were increased because of the improved mechanical properties and favorable flow fields.