Abstract: Planetary gear train (PGT) is widely used in machine tools and other equipment. Transmission efficiency is an important index to evaluate the performance of planetary gear train. However, at present, the phenomenon of unbalance load is not usually considered in the research on the transmission efficiency of planetary gear train, which affects the calculation accuracy of transmission efficiency for planetary gear train. Therefore, 2K-H planetary gear train is taken as the research object by the virtual power theory and a calculation method of power flow and transmission efficiency for planetary gear train is proposed for applying to multiple working conditions. According to the analysis results of dynamic model for planetary gear train, the calculation of results of transmission efficiency is verified, which provides theoretical guidance for the improvement of transmission performance for planetary gear train in the next step.