In order to explore the operation status of the energy storage battery when participating in the peak shaving/frequency modulation of the power grid, according to the actual operation condition of an energy storage power station in Zhenjiang, Jiangsu, a thermal model of the lithium iron phosphate energy storage battery module was established through finite element simulation. The experimental study of peak/frequency modulation cycle was further carried out, and the early capacity attenuation and temperature change data were analyzed to verify the temperature distribution of the simulation, and the operation rule under the mode of peak/frequency modulation was obtained. The results show that the average current ratio of the peak-loading mode is large, the battery temperature is maintained in a higher range, the maximum temperature difference is much higher than that of the frequency modulation mode, and the battery life attenuation is more obvious under the same charge-discharge capacity. The simulation can well reflect the variation trend of the internal mean temperature of the module, and the error is lower than 1.8 ℃, which meets the prediction accuracy, and can provide a safe design basis for the initial operation of the energy storage power station.