Modular multilevel converter （MMC） contains many power devices and large bridge arm current, which leads to large VSC unit operation loss and directly affects the system economy. To solve this problem, this paper proposes a strategy to reduce the switching loss of power modules, which reduces the switching loss by reducing the switching times in the area with higt bridge arm current, and suppresses the voltage fluctuation of modules by increasing the switching times in the area with low bridge arm current. Finally, taking the VSC unit in Liubei Station of Kunliulong Project as an example, the effectiveness of the loss reduction strategy is verified through PSCAD simulation and RTDS test, which significantly reduces the switching loss of power modules, and the system efficiency is improved.