Aiming at the problem of error between the actual value and estimated value of engine’s dynamic torque, as well as HEV’s energy control strategy cannot be executed accurately. Taken parallel-serial HEV as an example, the parameters of power coupling mechanism were analyzed. Planet gear power coupling mechanism’s dynamics characteristic and efficiency characteristic were applied to deduce the algorithm of engine output torque calculation method for parallelserial HEV. The experiment results showed that the maximum relative error of engine dynamic torque between theory calculating and experiment testing was decreased from 5%~8% to 3.94%. 