Battery energy storage system is widely concerned as an effective means to increase the renewable energy received capacity with its modular , fast response , flexible configuration , etc. The lithium battery energy storage power conditioning system and its optimal control is studied in this paper, the system parameters design scheme is given, a rule-based power optimization control strategy is proposed on the basis of power and the state of charge constraints to improve the life of lithium batteries, loop control that can be switched is used in the controller bottom to make the energy storage device reasonable charge and discharge strategy.The result of the experiment verify the correctness of the design parameters and effectiveness of the control strategy.