Abstract: The magnetic properties of permanent magnets are greatly affected by their operating temperature. Irreversible demagnetization at high operating temperature is the main bottleneck in high reliability design of permanent magnet motors. In order to solve the irreversible demagnetization problem of NdFeB permanent magnet for high power density permanent magnet motor with interior magnetic circuit structure, based on the difference of space loss and temperature distribution in the whole area of the motor, an analysis model and characteristic calculation method for local demagnetization of permanent magnet are proposed in this paper. The magnetic characteristic analysis model of permanent magnet material based on temperature, demagnetization and other variables is established by virtual block method of magnet. The spatial distribution characteristics of permanent magnet loss, temperature and local demagnetization of motor rotor are obtained by using the calculation method of bidirectional coupling of three-dimensional electromagnetic field and temperature field. Finally, the accuracy of analysis model and calculation method is verified by the test of permanent magnet temperature and magnetic field on rotor surface of a 115kW, 8-pole permanent magnet motor prototype, which provides basis for the research of permanent magnet motor local demagnetization problem and fine demagnetization protection design.