In order to achieve the three-phase current balance and voltage fluctuation suppression of railway traction systems, in this paper the phenomenon of voltage fluctuations of traction power arms is analyzed. A multilevel railway power conditioner based on four-leg chopper cells(FLCC-MRPC) is studied. The mathematical model of this FLCC-MRPC is derived and analyzed, and its comprehensive control strategy is proposed. This strategy can realize the negative-sequence compensation and voltage fluctuation suppression of the traction network. Simultaneously, it can reduce suppressors for 2nd harmonic circulating-current, and the 2nd line-frequency component of dc-bus voltage can be eliminated effectively. Through the simulations, the correctness and effectiveness of the control strategy are verified.