A method for charging a modular multilevel converter includes: firstly, electrifying DC side of a converter; after voltages of submodules are stabilized, deblocking the converter, turning on all the submodules, then reducing the number of turned on submodules in phase unit; when over-current occurs on a bridge arm, temporarily increasing the number of turned on submodules to suppress the over-current; after the voltages of the sub-modules are stabilized, continuously reducing the number of the turned on submodules until the number of the turned on submodules in the phase unit is finally equal to the number of working submodules of the bridge arm, so as to smoothly transit to a normal operation state. The DC side is charged, such that the voltages of the submodules reach a working voltage before the converter normally operates, and an impacting current is avoided in the charging process by using a proper control strategy.