Abstract: The embodiments of the present disclosure provide a battery state of charge prediction method and system. The method includes obtaining voltages and currents of a battery during charge and discharge; obtaining optimized model parameters with genetic algorithm by optimizing model parameters in a second-order RC equivalent circuit model of the battery according to the voltages and currents of the battery during charge and discharge; obtaining a cubic spline fitting function of state of charge of the battery, building a state of charge prediction model of the battery with extended Kalman filter algorithm according to the optimized model parameters and the cubic spline fitting function; predicting the state of charge of the battery according to the state of charge prediction model. The battery state of charge prediction method and system provided by the embodiments of the present disclosure can improve the prediction accuracy of the state of charge of battery.