Abstract: Due to the modular design, low output voltage harmonics, and easy scalability, modular multilevel converter(MMC) has been widely used in scenarios such as DC transmission. However, the DC fault is a key issue affecting the safe and stable operation. Therefore, in-depth research and simulation verification of its DC fault characteristics are conducted. Firstly, the topology and working principle of MMC are elaborated in detail, and based on this, the transient process of DC short-circuit faults and fault current analysis methods are studied. Then, a MMC model using MATLAB/Simulink is built to simulate DC faults, and the results are consistent with theoretical analysis, verifying the analysis conclusions of MMC DC fault characteristics. The research results can provide theoretical basis and technical support for the fault protection and control strategies of MMC.