This paper studies forward design technique for the rotor interference fit. Based on finite element method, the clearance values between the rotor and rotor hub generated by the maximum operating temperature and maximum speed separately were analyzed, the relation between the magnitude of interference and the resisting external torque for the rotor and rotor hub was studied, and the corresponding magnitude of interference was selected according to the maximum motor torque. Finally, the minimum magnitude of interference can be obtained by superposing the clearance value generated by the maximum operating temperature, the maximum speed and the magnitude of interference required to resist the maximum torque. The maximum magnitude of interference can be determined by the minimum magnitude of interference and manufacturing accuracy. The magnitude of interference requires no multiple adjustments and can be determined at one time by the method described in this paper, which improves the product development efficiency and shortens the product development cycle.