The variable cross-sectional rotor is considered as a potential technology to further improve the performance of twin-screw vacuum pumps, due to its remarkable advantages of large internal volume ratio. In this study, a mathematical model of variable cross-sectional rotors was established to obtain its generation method. A novel type of variable cross-sectional rotor was constructed by using the proposed method, and this rotor exhibits superior sealing performance. The variable cross-sectional rotor was geometrically compared with the traditional equal cross-sectional rotor. Then the accuracy of the proposed generation method as well as the advance of the generated variable cross-sectional rotor were verified by experimental test results. Results show that this design method achieves the construction of high accuracy variable cross-sectional rotors by generating 3-D helical surfaces. Compared with the traditional equal cross-sectional rotor, the geometric pumping speed and internal volume ratio of the variable cross-sectional rotor are increased by 7.57 % and 10.45 %, respectively. The volumetric efficiency of the variable cross-sectional rotor is increased by 6.52 % and the time to reach the ultimate pressure is reduced by 9.42 %, demonstrating superior pumping and sealing performance.