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 is analyzed and studied for the DC power supply servo drive system. Firstly, based on the working principle of permanent magnet synchronous motor (PMSM) and space vector pulse width modulation (SVPWM) algorithm, the ripple current of the busbar capacitor is 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 is analyzed theoretically, and its simplified expression is given. Finally, the theoretical results are verified by simulation experiments.