To solve the problems such as negative sequence, harmonics and reactive power in the traditional railway traction power supply system, model predictive direct power control (MPDPC) is introduced to the railway power conditioner with modular multilevel converter (MMC-RPC) structure based on direct power control. The objective function is determined according to the principle of minimizing the power error at the end of each control cycle and delay compensation is added to the traditional MPDPC to obtain the optimal voltage vector at the AC port of MMC-RPC. A simulation model of MMC-RPC based on MPDPC is built in Matlab/Simulink, and it is compared with MMC-RPC which is based on direct power control and double closed-loop PI control, thus verifying the superiority and feasibility of the application of the MPDPC strategy to MMC-RPC.