The impact of H-bridge parameter differences on the DC capacitors’ voltage is analyzed in this paper based on the static mathematical model of DC capacitors’ voltage of cascaded static synchronous compensator (STATCOM). According to the problem of DC capacitor’s voltage unbalance caused by H-bridge parameter differences, a novel balancing strategy is proposed based on optimal allocation of pulse, which can solve the problem of DC capacitor’s voltage unbalance caused by H-bridge parameter differences, and can make capacitors’ voltage balance quickly in the premise of no change of switching frequency of power component and output voltage, so as to improve the output performance of cascaded STATCOM and system reliability. The principle and characteristics of a novel balancing strategy based on optimal allocation of pulse are analyzed, and a prototype of 380 V, 10 kvar cascaded STATCOM had been developed to verify the theory analysis.