Battery management system (BMS) which measures battery status with high accuracy has a critical effect on the performance of power battery and the entire car. To solve the problem of identification precision decreasing for the reason of BMS asynchronous sampling, the original computing method is improved by using gradient adjustment method and based on order 2 RC battery model. A simulation is performed by using Simulink, the identification results between the original computing method and improved one are compared, the precision of the latter is better than the former under the condition of current sampling time point after voltage sampling.