The global energy crisis and serious environmental pollution make governments attach importance to the development of regenerating green energy. As the best battery system at present, lithium-ion battery has developed rapidly into a new generation of energy storage power. SOC estimation is an important indicator in the development of lithium-ion batteries. If SOC can be properly estimated, it will be pivotal to the investigation and exploitation of batteries, and a number of algorithms for SOC estimation have already emerged. This paper first introduces several current SOC estimation methods, and then explains the influencing factors and hysteresis effect of SOC. Then the SOC estimation value was obtained by open circuit voltage method, based on the mean value calculated by the random forest output OCV-SOC curve to reduce hysteresis effect. The effect of temperature on SOC was analysed by plotting the OCV-SOC profiles for charging and discharging at different temperatures. Finally, this paper is summarized and puts forward the improvement.