In the context of the “dual carbon” goals, to address issues such as high energy consumption, high expenses, and low power quality encountered in the rapid development of electrified railways, this study focuses on the CRH2 electric multiple unit (EMU) and proposes a dynamic simulation model of an on-board energy storage system based on a locomotive-traction network co-simulation platform. The model employs lithium batteries and supercapacitors as energy storage media, utilizing voltage-following and logic gate control strategies for each medium, respectively. Using typical working conditions as examples, the control strategies and correctness of the model for the energy storage system are validated. The results demonstrate that the on-board energy storage system can stabilize the DC bus voltage of the EMU and achieve peak shaving and valley filling for the traction load power demand.