In order to improve the anti-disturbance performance and achieve more accurate control effect of MMC-RPC, a dynamic mathematical model was established for the railway static power conditioner (RPC) by using the modular multilevel converter (MMC) structure. Based on the introduction of differential flatness control theory (FBC), two set of outputs were selected from the dynamic mathematical model of MMC-RPC, which enabled MMC-RPC to meet the conditions of the differential flatness system. The structure of the FBC controller had two parts, i.e. feed forward control and error compensation respectively, with cascade connection. The outer loop generated a flat output which was the reference trajectory, and the inner loop generated the d and q axis voltage components which were the expected output of MMC. The simulation result of the MMC-RPC system which was controlled by FBC and PI in 3 working conditions verified the validity and superiority of the FBC control system.