As a bridge of the transmission system, flexible DC transmission line plays an important role. If a fault occurs, it will bring serious consequences to the entire transmission system. It is very important to study the fault location of the flexible DC transmission line. According to the system structure of flexible DC transmission line, the mathematical model, operation mode and control strategy of MMC are analyzed. According to the characteristics of transmission line with bipolar short circuit fault, a fault location method based on BP neural network is proposed. Combined with PSCAD/EMTDC, a twoterminal flexible DC transmission system is built, and the fault data of the flexible DC transmission line is obtained by simulation. After preprocessing the data, a sample set is constructed. The neural network analysis uses the two-terminal fault location method, and finally a high-precision fault location model is obtained, which verifies the accuracy and effectiveness of the location method proposed in this paper.