To mitigate the power quality issue of traction power system caused by locomotives and maintain a clean and safe power grid， a railway power static conditioner is discussed. As the railway locomotive is random and fast， an improved one-cycle control method based on equivalent resistance feedforward control is presented. The equivalent load feedforward control can track the variations of load in real-time， which effectively improves the dynamical performance of the control system. The PI control of DC-link voltage can maintain a stable DC-link voltage and ensure the normal operation of railway static power conditioner. In order to overcome the dead-time effect， a dead-time compensation method is adopted to enhance the compensation accuracy. Finally， simulation and experimental results verify the correctness of the proposed control method.