A system and method for reducing drive motor speed ripple of an electric vehicle are provided. The system includes an inverter that converts DC power supplied from a battery to AC power and supplies the AC power to the drive motor by inverter switching. A resolver is configured to detect a speed of the drive motor and a position of a rotor, a signal generator includes a microcontroller that is configured to generate a square wave signal. An integrator is configured to convert the square wave to a sine wave, and apply a sine-wave excitation input signal to the resolver. Furthermore, a motor controller is configured to operate the inverter through a PWM signal, adjust the frequency of the excitation input signal to prevent the inverter switching frequency of the inverter and the peaks of an output voltage signal sampled for speed calculation from overlapping.