Virtual synchronous generator provides inertia and damping support for the system by simulating the external characteristics of the VSG, so that the inverter system can run safely and stably. Due to the existence of nonlinear load in the new energy inverter system, the output harmonics of the system are polluted, which affects the output power quality. In order to optimize the system output, this paper combined with VSG control algorithm, introduced a random excitation in the noisy system PWM modulation wave, and then compared with the carrier to generate the driving signal. The harmonic distribution is analyzed by voltage power spectral density. Simulation results show that the random excitation method is adopted to VSG inverter output voltage waveform is improved to a certain extent, compared with before introducing random excitation, the output of A, B, C threephase voltage total harmonic factor（THD）was reduced by 11.32%, 11.60% and 11.42%, respectively, show the rationality and validity of this method and suitable for engineering applications.