In view of the grid voltage imbalance under HVDC transmission, the traditional control strategy adopts separate suppression of negative sequence current and power fluctuation, which increases the difficulty of control and reduces the quality of the grid. Therefore, for the problem of grid voltage imbalance, the power adjustment factor was firstly introduced to realize the coordinated control of current and power. Furthermore, the proportional reduced-order vector resonance controller (PI-ROVRC) was used as the current inner loop control. The propor- tional -integral controller realized the static -free control of the DC component of the grid current, and the ROVRC performed the tracking control of the AC component in the grid current without difference, thereby im- proving the current quality of the MMC AC side. The overcurrent problem on the AC side was further discussed when the grid voltage was unbalanced. The method for correcting the active power command value was applied to limit the current amplitude at the fault to a specified range, improving the dynamics and reliability of the sys- tem. Finally, the simulation was verified by PSCAD/EMTDC simulation platform. The results showed that the proposed control strategy was consistent with the simulation, which proves the feasibility and effectiveness of the proposed scheme.