The load capacity of the permanent magnet synchronous motor is limited by the rotor temperature, and the excessive temperature of the rotor will bring potential thermal safety problems of the system. Therefore, the accurate prediction of the rotor temperature of the permanent magnet synchronous motor for the electric vehicle is crucial to improve the motor performance and system operation safety. This paper studied the heating mechanism and the energy flow path of the motor and built the heat energy conversion model of the stator and rotor. The real-time algorithm to predict the rotor temperature was constructed based on the dissipative energy conservation of the stator of the motor rotor temperature. And the prediction method of the initial rotor temperature is fitted using the experimental results when the system is powered on. Finally, the test platform was set up to validate the rotor temperature accuracy. The results show that the motor rotor temperature estimation error under the dynamic operating condition is within ±5. The research provides a solution to improve the performance and thermal safety of the permanent magnet synchronous motor for electric vehicles.