The integration of energy storage systems (ESS) into railway traction power supply systems (TPSS) presents a promising approach to enhancing energy efficiency in modern electrified railways. This paper proposes an energy management strategy for electric railway system with the integration of ESSs, which achieves effective peak shaving, enhances energy utilization, and reduces electricity cost. A combined model incorporating train trajectory optimization, traction system power flow calculation, and ESS behavior is established to jointly optimize ESS location, sizing, and operational strategy. At last, the proposed method is validated on a Swedish railway case study to demonstrate improved energy management performance under realistic conditions.