The invention provides a charging method of an MMC current converter for testing. A direct-current energy-supplementing power supply has been used before a direct-current charging power supply exits and is maintained in a working state, so that rapid switching can be realized after the direct-current charging power supply exits, and direct-current support can be provided for operation of the current converter; meanwhile, a voltage at the two ends of a capacitor is guaranteed to be in a constant range, so that a system can run stably, and the problems that the required switching time is relatively long because the direct-current energy-supplementing power supply is started after the direct-current charging power supply exits, and the voltage at the two ends of the capacitor cannot reach a rated voltage of an MMC sub-module due to energy loss of the current converter are solved; and moreover, a circuit is simple in structure and easy to realize.