In the paper, to reduce the DC-link capacitor voltage harmonics of dual-cascading PWM rectifier in electric traction AC drive system, firstly, the theoretical design method of DC-link capacitor was introduced, then, the characteristic of high order harmonics of DC-link voltage in the steady-state was derived, and DC link voltage ripple of the dual-cascading PWM with carrier phase-shifting technology was analyzed in detail. The theoretical analysis showed that the high order ripples of DC-link voltage were mainly distributed around the twice switching frequency, and the carrier phase-shifting technology could reduce these high order ripples to suppress the DC voltage ripple coefficient. Therefore, the DC-link capacitor could be minimized based on traditional design method in combination with carrier phase-shifting technology. Control methods with and without carrier phase-shifting technology were compared in computer simulation and hardware-in-theloop( HIL) experiment system respectively, which showed the validity and effectiveness of theoretical analysis.