The method of using special form instead of general form for the analysis of dual planetary gear mechanism is proposed in order to utilize the velocity graphic method effectively.The process of using velocity graphic method to analyze the transmission scheme of dual planetary gear mechanism is optimized through drawing the linear velocity vectors of the constant velocity point
and the calculation of transmission ratio is predigested.The correctness and universalism of the optimization method is verified by the transmission ratio calculated by comparing the velocity graphic method with analytic method.