The design method of screw rotor based on meshing method and NURBS curve is proposed. In the process of the designing, the formula of the quadrature was obtained. This paper solveed the envelop condition of NURBS curve, and realizes the reverse design of the whole line of NURBS curve which was determined by the control point, weight factor and node vector. Through this method, the compound line of the error was obtained within 0.5 μm microns and the relation between the performance and meshing lines is explored. The feasibility of reverse design of screw rotor by using NURBS curve wes verified. Using the local modification of NURBS curve to optimize the type line, the leakage triangle area of the rotor was reduced by 5%, and the area utilization coefficient increased by 1%. The theory and method for the optimization design of rotor line of double screw compressor is provided.