The switching of power devices in servo drive can lead to bus voltage ripple, which may result in performance degradation, electromagnetic interference, and harmonic issues in permanent magnet synchronous motor AC servo systems. To address these issues, the influence of the switching process of power device on the voltage ripple of bus was analyzed and studied for the DC power supply servo drive system. Firstly, based on the working principle of PMSM (permanent magnet synchronous motor) and SVPWM (space vector pulse width modulation) algorithm, the ripple current of the busbar capacitor was analyzed. Then, according to the law of charge conservation, the relationship between the busbar capacitance, busbar voltage and current amplitude under the seven-stage and five-stage SVPWM modulation was analyzed theoretically, and its simplified expression was given. Finally, the theoretical results were verified by simulation experiments.