Power battery system is widely used in new energy vehicles. The performance of power battery directly affects the safety of new energy vehicles. At present, the research of battery system safety focuses on a specific parameter such as the status of charge (SoC), the state of health (SoH) and so on. However, a single performance evaluation may lead to some defects in system safety. The influences on the power battery system of SoC, SoH, and the status of consistency, which are essential factors in battery system safety, were analyzed in this study. In view of the conclusion of the analysis result, the concept of the power battery system performance matrix, which includes the parameters of SoC, SoH, the status of consistency and temperature, was proposed. The state-space expression was studied and used for the expression of the performance matrix. Cyclic charging and discharging experiments of Lithium-ion batteries were carried out, and the result showed that performance matrix based on state-space could describe the dynamic changes of battery system status. It was sufficient for the estimate of the battery system's safety status, and it can provide the effective and reliable data resources for the system maintenance.