The ultra-high-speed permanent magnet synchronous motor (PMSM) has the characteristics of high speed and relatively low tensile strength of permanent magnets. Therefore, it is necessary to set a sleeve on the outside of the permanent magnet of the rotor，and generate radial compressive stress on the permanent magnet through interference fit, so as to offset the centrifugal force generated during the rotor high-speed rotation and protect the permanent magnet. A method for calculating and analyzing the thickness and interference of rotor non-magnetic alloy sleeve of the ultrahighspeed PMSM is proposed. Taking a 120 000 r/min ultra-high-speed PMSM as an example, the coupling simulation of temperature field and rotor statics is carried out by using finite element method, and the numerical method is verified. The optimized design is utilized to reasonably calculate the thickness and interference amount of the sleeve under the condition that the motor rotor meets the requirements of structural strength. It can effectively reduce the thickness of rotor sleeve, thus reducing the iron consumption of rotor，which provides a reference for rotor design of ultra-high-speed motor.