To further estimate the accuracy of lithium-ion battery accurately, the E-SOC curve is obtained based on the theory of constant current discharge method and Thevenin equivalent model. SOC of lithium-ion battery pack is estimated. Based on DBN and experimental data, SOC of lithium-ion battery pack is estimated. The simulation results show that the proposed method can predict the trend change of SOC within the allowable error range and effectively improve the estimation accuracy of SOC.