Abstract: The shell or frame of the battery system is directly grounded and there are parasitic capacitors, which leads to the common mode voltage and current effect of the positive and negative terminals of the battery system on the ground. The common mode voltage and current problems become the main factors affecting the insulation of the battery system. Based on the existing integrated architecture of energy storage system, common mode voltage and current of battery system are studied in this paper, and a second-order common mode equivalent circuit model suitable for energy storage system is established. Quantify the characteristics of common mode voltage and current of the battery system and the change rule under the influence of parasitic capacitance, switching frequency, and other factors. The simulation and experimental results show that the common mode voltage and current are the main factors affecting the electrical characteristics of the battery system to the ground, which provides technical support for the optimal design of the system.