The high-speed permanent magnet motor has compact structure, high power density and difficult heat dissipation, which would easily cause irreversible demagnetization of the rotor permanent magnet due to excessive temperature rise. Taking a high-speed permanent magnet motor with the rated speed of 30 000 r/min as an example, based on the principles of computational fluid dynamics and numerical heat transfer, from the perspective of practical engineering applications, the wind friction loss of the rotor and temperature rise are calculated and analyzed under different ventilation rates, and compared with the motor temperature rise test results. The research shows that the wind friction loss of rotor accounts for a large proportion of total wind friction loss in the high-speed permanent magnet motor, and the proportion increases with the increase of flow rate. After the ventilation rate reaches a certain value, the heat dissipation of the motor reaches a balance, and the wind friction loss of the rotor increases sharply with the increase of flow rate, which causes the temperature of the permanent magnet to rise. After using water cooling for the motor base, the ventilation rate can be reduced, so that the motor can reach the ideal temperature rise level.