In this paper, we have utilized battery capacity tests and hybrid pulse power characteristic (HPPC) tests to ascertain the internal parameters of a sodium-ion battery model, taking into account varying aging levels, temperatures and states of charge. This paper discusses the foundations of model selection and focuses on methods for identifying the relevant parameters. The specific factors affecting the changes of battery capacity and internal resistance are analyzed, and the influence of temperature effect on the parameters is fully taken into account to correct the usable capacity of the battery and optimize the traditional equivalent circuit model. Based on the circuit model theory and experimental data, the second-order equivalent circuit model of sodium-ion battery is established, the effects of temperature and SOC on its parameters are revealed, and the effects of battery aging on various parameters of the battery are also analyzed and investigated, which provides an accurate underlying battery model for the subsequent research of sodium-ion battery.