Magnetic steel is relatively fragile,so to ensure the structural strength of magnetic steel in a safe range is a key point in the design of a highspeed motor.The pressure generated by the interference fit between the sleeve and the magnetic steel can ensure the safety of the highspeed motor magnetic steel.In order to ensure the safe operation of the motor,the thickness of the sheath and the interference must be calculated and checked according to the rotor speed,outer diameter and other parameters.Three kinds of common magnetic steel structures were compared and the solid cylinder structure was chosen;through calculation and analysis,the method to choose the material,thickness and interference of the sleeve was obtained.Considering the centrifugal force and interference fit,the rotor of a 70 000 r/min permanent magnet synchronous motor was analyzed and designed.The research results provide reference for the design of magnetic steel and sleeve of high speed permanent magnet motor.