Abstract: With the rapid development of high-speed railway, the problem of energy saving and carbon reduction has attracted much attention. Using green energy for traction power supply is an effective way to save energy and reduce consumption. If a large amount of regenerative braking energy of high-speed railway is reasonably reused, waste energy can be turned into green energy, and the energy consumption of traction power supply system can be promoted to be clean. This study focuses on capacity optimization of hybrid energy storage systems for recovering regenerative braking energy in high-speed railways with long steep slopes, where photovoltaic (PV) systems are integrated into the traction power supply. Based on comprehensive analysis of green power resource acquisition patterns, PV generation characteristics, and braking energy features, while considering the power characteristics across different time dimensions and energy profiles under various operating conditions in green traction scenarios, we propose a segmented configuration scheme for the hybrid energy storage system. The proposed approach utilizes energy storage demand density to efficiently recycle both regenerative braking energy and photovoltaic power. According to the characteristics of different energy storage media, their respective optimization models are established, and the improved simulated annealing algorithm based on Levy flight (LESA) is used for optimization. Finally, the measured data of a traction substation of Xi'an-Chengdu high-speed railway are selected for example analysis. The example results show that the proposed optimal configuration strategy, taking into account the photovoltaic energy and regenerative braking energy, completes the optimal configuration of the capacity of the high-speed rail long steep slope hybrid energy storage system, effectively improves the proportion of green energy in the traction power supply system, and shortens the cost recovery period of the energy storage system, which can provide reference for the engineering application of high-speed rail energy storage system, and promote the green and low-carbon development of rail transit traction energy.