Abstract: The lithium-iron phosphatebattery is studied in this paper. The equivalent circuit model is established and the characteristics of model parameters are analysed. The double Kalman filtering algorithm is presented to estimate the cycle life of battery pack, which is defined as State of Health (SOH). The efforts of our study are, firstly the parameters and state of charge(SOC) are estimated based on robust Unscented Kalman filter (R-UKF). Secondly, the SOH value is estimated using Extended Kalman filter (EKF) according to real-time value of the model parameters. The experimental results indicate that our new algorithm can obtain the estimation results more accurate. Besides, our studies have important application value for improving the energy storage capacity, utilization ratio and cycle life of the integrated battery.