The invention relates an MMC-MTDC system starting control method comprising the following steps that A. the DC side poles of all converter stations are connected, the submodules of all the stations are locked, and the AC switch of an active station is closed so as to enter an uncontrollable charging stage; B. after voltage of the submodules of all the converter stations is higher than respectively corresponding charging threshold voltage, a controllable voltage equalizing charging method is switched on by the converter stations respectively and a controllable charging stage is initiated, and the AC side soft starting resistor of the active station is removed simultaneously; and C. when the station control mode is that voltage of the submodule of the constant DC voltage controlled converter station is rated and stable, the converter station enters an unlock operation stage firstly; and when voltage of the submodules of the rest stations is rated and stable, the stations are unlocked respectively and enter the unlock operation stage. The constant DC voltage controlled station is unlocked firstly so that voltage of a DC bus can be stabilized and thus stable operation of a multi-terminal system can be ensured.