With the increasing penetration of power electronic devices in the grid, which make the whole system unstable, virtual synchronous generator (VSG), as a new control strategy, can simulate the characteristics of traditional motors and make the system inertial and damped. It get a wide range of concerns. In this paper, virtual synchronous rectifier is analyzed with mathematical model. Under the condition of grid voltage unbalanced, the virtual synchronous generator control strategy is improved in for the purpose of stable DC voltage. The simulation results based on Matlab/Simulink are verified, which simulate the operation of power fluctuation and three-phase unbalance. The simulation results verify the correctness and validity of the proposed method.