In order to improve the assessment accuracy of power battery health degree, this paper provides an assessment arithmetic based on power battery life cycle characteristic parameter for power battery box (group). Starting with the safe use and accurate assessment of power battery, concerning the SOC arithmetic and SOH test methods of power battery, it leads to the design concept of on-line monitoring supervision system for power battery life cycle; with the power battery nominal data as basis, it tests the power battery based on its daily charging/switching and discharging data, to conduct unified management of power battery with hidden danger during testing and make battery maintain/servicing plan. The assessment result shows that with battery box (group) as analyzing/managing object, assessing battery box with corresponding strategies according to power battery electrical features, we can assess the current health condition of power battery relatively accurately, and forecast the use tendency of power battery, thus achieving the goal of improving the security of power battery use, prolonging its serving life and reducing the operating costs.