Accurate analysis of the thermal field in switched reluctance motor (SRM) is critical to the service life and safety performance of the SRM. According to the general structure of SRM, a twodimensional (2D) finite element analysis (FEA) model was established, and the loss of each component, especially the iron loss, was analyzed by Orthogonal Fourier decomposition method, revealing the characteristics of the loss. A magnetic-thermal one-way coupling method is further used to model the temperature of the SRM, and basic assumptions and reasonable boundary conditions are set. Transient thermal analysis was carried out under natural cooling conditions and high vacuum conditions, respectively, and the results were compared and analyzed to understand the temperature distribution of the main components under two operating conditions.