A design method for the rotor profile of twin-screw compressor from an arbitrary sealing line is presented. The sealing line is divided into several functional segments that control the high-pressure side and the low-pressure side performances independently. Each functional segment is fitted by cubic spline and the shape of the segment can be adjusted by moving the control points of the cubic spline. Based on the shape of the sealing line, the performance of the compressor can be directly calculated and the corresponding rotor profiles are derived considering the non-undercutting condition. A numerical example which considers the geometric constraints of rotor profiles is presented to demonstrate the flexibility and stability in parametric study of the rotor design.