For over current in converter bridge arms before blocking in case of DC short-circuit faults in MMC-HVDC system, a method based on coupled bridge arm reactors is presented, which can effectively suppress fault current, and improve the steady state operation of the system. This paper establishes the MMC-HVDC system model with coupling bridge arm reactors and expounds the coupling principle of reactors. Then fault current is analyzed and the best coupling coefficient is selected. Finally a 31-level MMC-HVDC system is established in MATLAB, and the parameters of system based on coupled bridge arm reactors are compared with that of system based on ordinary reactors in the two phases of normal operation and fault. The result shows the validity of the proposed method. This work is supported by National Key Research and Development Program of China (No. 2016YFB0900903).