The disequality of cells in the same battery team is one of the main factors influencing on the performance of satellite power system. This paper discussed the disequalization of a battery,and established a mathematical model.Based on the model, a new method to control battery equalization was present to counterpoise the energy of in the same battery team in series both for charging state and discharging state. The design ideas and design schemes of the hardware and the software of this equilizer were introduced in detail and the software flow charts of equalizer in charging state and discharging state were given. Finally an experiment was carried out to testifly that the method can decrease the inequality of in the same battery team to 13.42 %(charging) and 9.39%(discharging) as compared with those of battery systems without equalization.