MMC-VSG grid-connected systems are widely used in renewable energy generation systems to actively support the power grid. During the grid-connection process, if the amplitude, frequency, and phase deviation of the MMC output voltage from the grid voltage are too large, it can result in excessive grid currents, which may lead to grid-connection failures and damage to circuit components. To address this issue, this paper proposes a pre-synchronization control strategy for MMC-VSG systems. The phase relationship between the inverter output voltage and the grid voltage in the rotating coordinate system is obtained through coordinate transformation, the phase difference between the two is calculated, and after PI control adjustment, the compensation value of the grid-connected phase angle frequency is obtained, so that the phase amplitude and the voltage of the inverter side and the grid side remains consistent. A VSG based off/pre synchronous grid model was built using MATLAB/Simulink, and the simulation results verified the correctness and superiority of the proposed control strategy.