Abstract: The paper analyzed generating mechanism of CMV of cascade multilevel converter with a three-phase equivalent circuit in details and introduced harms to high power converter and frequency-conversion speed-regulation system caused by CMV. Then it discussed researching situation of suppressing CMV at present and analyzed characteristics and disadvantages of suppressing CMV methods with hardware named adding filtering equipments and changing converter's structure and suppressing CMV method with software named control strategy, so as to provide some reference for researching a new strategy to suppress CMV. At last, it proposed some future research targets of suppressing CMV of high power converters: firstly, it is important to find an optimal suppressing CMV method which can take account of utilization of DC voltage and harmonic content; secondly, it is necessary to find a unified algorithm for completely eliminating CMV which is suitable for all topologies.