Contraposing the problem that the still standing open circuit voltage was unstable after the hybrid electric vehicle was charged in the running process, especially in regenerative braking process, which resulted in the great error in the SOC estimate for open circuit voltage method and difficulty in implementation of the power control strategy for hybrid electric vehicle, the lithium iron phosphate battery, as a research object, was analysed in the influence mechanism about the electrode surface lithium ion diffusion and open circuit voltage that was time-varying according to theory of electrochemistry. And the still standing voltage forecasting model for lithium iron phosphate battery was established by still standing experiment and parameter identification. The prediction by the model in the prediction experiment showed that the biggest prediction error was 0.017V in the experimental operating conditions.