This paper researches the principles of eddy-current losses of permanent magnet synchronous motor. Firstly, the paper establishes an analytical model of the flux density in magnets and eddy-current density from the point of views of eddy field and harmonic model. At the same time, the comparison of FEA and analytical result are put forward. In order to analyze the influence of eddy-current losses to the stability of high power-density and different magnet structure to the temperature rise of PMSMs, the paper provides the thermal
analysis of prototype motor. It is shown that the analysis results can provide directive value for motor design and stability analysis.