Abstract: Herein,we addressed the clearance design and machining,with two regular NC lathe turning tools,of a fixed-pitch screw rotor,a core component of screw vacuum rotor pump.The original work was the two-step machining.First,the coordinates,of the cutter position point of the axial section of rotor shaft,were derived according to the feed-rate;second,the groove's concave and convex sidewalls were machined,respectively;third,the thermal deformation distribution of the screw rotor were simulated with ANSYS software to determine the axial bevel and concave cutting clearances for satisfying the gap requirements;and finally,a dedicated program was developed by means of NC lathe micro-program,and the variables of cutter position point coordinate simplified the program.We suggest that the newly-developed machining scheme be of some technological interest in fabrication of other types of screw rotor.