Cogging torque ripple is the main impact factor of the output torque ripple of electric vehicles driven by wheel hub motors. To suppressing cogging torque ripple, a DC external rotor motor was studied, and a finite element analysis model was established in Ansoft Maxwell according to its structural parameters. The simulation results of cogging torque agreed well with those obtained from experiments, and this showed the analysis model was correct. Then, the main parameters of the hub motor were optimized by using Taguchi method, in which the peak values of cogging torque and average values of output torque were taken as the optimization goals, the slot width, pole arc coefficient, air gap length and parallel tooth width as the control factors, the processing errors of notch width, air gap length and parallel tooth width, and residual magnetism variation as noise factors. The performances of the motor were simulated in the finite element analysis model with optimal structural parameters. The results showed that the cogging torque of the motor was reduced significantly, and the average values of output torque were increased slightly at the same time.