Because of the large capacity, low cost and low self discharge advantages,Lead acid batteries is becoming the basic components of the the emergency power supply (EPS) system.And the residual capacity as the important measure of battery capacity index directly affects the safe operation of the system.This article introduce the battery terminal voltage and internal resistance of the two parameters as the capacity of two associated factors to establish and improve a link between multiple factors analysis of gray model GM (1, N).After that,we proposes a reasonable and effective selection method of parameter which is influence the amount of key model prediction precision weighted average sequence parameters.The final prediction example verification and error analysis show that the method has simple operation, low algorithm complexity and the advantage of high precision, strong practical application value.