There is a transient overvoltage problem caused by the active and reactive power interaction coupling of the rectifier when a fault occurs in the sending end AC system. First, the main influencing factors for DC power and reactive power consumed by the rectifier are clarified, and the coupling relationship between reactive power consumption and DC power of the rectifier after commutation failure (CF) caused by a sending end AC system fault is analyzed. It is concluded that the relationship between reactive power and DC power is negatively correlated during the rising stage of DC current, and the relationship is positively correlated during the falling stage. Secondly, the influencing factors of the transient voltage amplitude during the fault recovery period are analyzed, and the transient overvoltage mechanism considering the interaction coupling of active and reactive power under different fault severity is clarified. Then, the mathematical relationship among the unbalanced active power of the sending end system, the reactive power consumed by the rectifier and the DC current is established. Based on the mathematical relationship between the reactive power and the bus voltage, and considering the interaction coupling relationship between active and reactive power, a transient overvoltage control strategy considering the active power support is proposed. Finally, the simulation results based on PSCAD/EMTDC verify the accuracy of the theoretical analysis and the effectiveness of the proposed control strategy.