Abstract: Modular multilevel converter based multi-terminal DC transmission (MMC-MTDC) system can realize multi-source power supplies and multi-terminal power-receiving. Flexible in operation modes, it is thus an effective technical means to solve the problem of grid-access and accommodation of clean energy. However, when AC fault occurs at the AC side of the receiving-end system, the created surplus power of the system will lead to serious DC overvoltage. In view of this, this paper proposes a DC overvoltage suppression strategy for multi-terminal flexible HVDC system based on bridge arm modulated wave dynamic adjustment. The proposed strategy introduces DC voltage deviation control into the modulation wave of the converter valve bridge arm, dynamically adjusting the DC voltage reference value of the bridge arm modulation wave during transient periods, thereby reducing the number of sub modules invested in the bridge arm, and ultimately achieving the goal of suppressing DC overvoltage. In order to verify the effectiveness of the proposed control strategy, a four-terminal flexible HVDC transmission system for photovoltaic and hydropower transmission is built in PSCAD/EMTDC, and the parameter design method of the proposed control strategy is given. Finally, by setting different operating conditions for the receiving-end AC system, a comparative study is made on the DC overvoltage characteristics of the system after implementation of the proposed control strategy. The results show that the proposed control strategy can effectively suppress the DC overvoltage of the MMC-HVDC transmission system caused by the receiving-end AC-side fault.