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The DC capacitors' voltage balancing strategy is one of the key technique of cascaded H-bridge STATCOM, because the DC capacitors of cascaded H-bridge STATCOM playing an important role in supporting DC voltage. The impact of H-bridge parameters on the DC capacitors' voltage has been analyzed based on then static mathematical model of DC capacitors of cascaded STATCOM. And traditional pulse rotation control method can make capacitors' voltage balance in the premise of no change of reactive current's THD. But this method has the disadvantage of capacitors' voltage balance slowly and bad steady performance. According to the advantages and disadvantages of traditional pulse rotation control method, an optimization pulse rotation control method is proposed in this paper to overcome the shortcoming of capacitors' voltage balance slowly and bad steady performance by pulse rotation control method. And the principle and characteristics of this optimization strategy is analyzed. Simulation mode of 11-level cascade STATCOM has been developed to verify the theory analysis.