Abstract: With the integration of large number of distributed power sources and DC loads, the DC distribution system has more advantages than AC system. Fault location is one of the key supporting technologies for reliable and high-quality power supply of DC distribution network. This paper analyzes the transient characteristics of the pole-to-pole short-circuit fault in the modular multilevel converter（MMC） based flexible DC distribution network and proposes a precise fault location method based on the transient current at the initial stage after the blocking of the sub modules. The equivalent circuit of two-terminal MMC based flexible DC distribution network is established. The time-domain expression of DC current is derived, the time-domain equations including two unknown parameters of fault distance and transition resistance are constructed, and the least square method is used to solve the equations. The method is suitable for different grounding modes. In PSCAD/EMTDC, a two-terminal flexible DC distribution network model is built. The simulation results verify the effectiveness, reliability and accuracy of the method. The proposed method also has high location accuracy for the scene of asymmetric parameters and time-varying transition resistance of converter stations at both terminals.