The invention relates to a method for suppressing overvoltage between current converter bridges and a system thereof. A widely applied 12-pulse series-structured current converter structure is arranged in an ultrahigh voltage direct current project. In the unlocking process of the actual project, the trigger angle of a 12-pulse valve group probably has deviation, 24 times of harmonic wave is excited, and resonance is caused in a current converter loop by the 24 times of harmonic wave and relatively high overvoltage is generated between the current converter bridges. The size of overvoltage between the current converter bridges is detected firstly and compared with the set threshold value. If the size of overvoltage is greater than the set threshold value, a direct current filter is enabled to be disconnected before unlocking of the current converters next time, the loop of the 24 harmonic wave in the current converters is cut off and generation of overvoltage between the current converter bridges is suppressed. The method is effective, simple and convenient, normal unlocking is performed by overvoltage is suppressed and degree of complexity of a direct current power transmission system is not increased.