This paper proposes an advanced filter design to improve power quality of a head electric power (HEP) as a power conversion unit in centralized-power type electric railway vehicle. First of all, we have measured waveform of output power of transformer connected HEP to design the filter. Throughout experiment and simulation results, it is estimated that switching technique used HEP is advanced selected harmonic elimination PWM (SHEPWM) and the applied switching frequency is about 300Hz. In this paper, a filter to improve power quality considering estimated parameters is designed. As a result, the reduction of the magnitude of the overall harmonic is achieved and confirmed through simulations.