When using PI controller, overshoot of speed was prone to occur during the motor startup process. To solve the problems of overshoot and slow tracking in the startup process of series multiphase motor system, an improved active disturbance rejection controller (ADRC) to substitute PI controller in the series system of asymmetric sixphase dual permanent magnet synchronous motors (PMSMs) was studies. Then, the genetic algorithm was introduced to optimize the module parameter of proposed method by optimization criterion of minimum overshoot. Finally, an asymmetric sixphase dual PMSM series system based on improved ADRC was built in MATLAB/Simulink. The simulation results showed that the method used had fast adjustment and accurate tracking effect, compared with the traditional PI control. In the meantime, the influence of harmonic current and torque ripple could be well weakened. All of these verified the practicability of this control strategy.