With the continuous development and application of new energy technologies of power system, power electronic technology of power conversion and control is becoming more important. And the temperature is one of the main factors affecting power electronic equipment performance. ANSYS is finite element analysis software with powerful functions in thermal analysis. Fundamental principles and methods of ANSYS thermal analysis are introduced, then analyses the power electronics devices' temperature and its transmission in this article. And obtain temperature field distribution; this is very important for the reasonable design of the heat dissipation for the power electronics devices.