Aiming at solving the problems of negative sequence current and voltage second harmonic in modular multilevel rectifier affect system stability under an unbalanced power grid voltage condition, a control strategy has thus been proposed based on the combination of signal delay method and dual current inner loop control, taking into consideration the large active power disturbance and the second harmonic found in the DC side voltage of the rectifier. Based on the current instruction algorithm, the positive and negative sequence components of current can be separated and calculated. By using PI regulator, no static error control of positive and negative sequence current can be achieved, thus effectively reducing the disturbance of active power p(ωt) and restraining the second harmonic of DC side voltage of the rectifier. The simulation results show that the proposed control strategy exhibits a favorable suppression effect.