A reliable and reasonably accurate loss model of variable speed motor systems is important for its performance prediction and energy consumption analysis. Most of the existing methods are based on the finite element analysis, but the disadvantage lies in the computational difficulty, which is not suitable for practical application. A practical simulation model of variable speed motor systems based on MATLAB/Simulink was estabcished. The converter losses were calculated by analytical model of IGBT and Diode, and the iron lossed in variablefrequency motor was considered as variable iron loss equivalent resistance. The efficiency of the motor system under different conditions was analyzed, and it showed that traditional models of motor systems may cause errors when determining the optimal system operating point, with the converter losses neglected. The experimental validation was also performed on a 5.5 kW motor. The achievement coucd provide technique support for the optimal control strategy for motor systems.