Abstract: This paper uses the bacterial foraging algorithm（BFA）to solve the optimal sizing problem of hybrid energy storage in Wind/PV complementary power generation system. The full life cycle cost of hybrid energy storage device is built with the constraint that takes the reliability index of loss of power supply probability (LPSP) and loss of produced power probability (LPPP) into account in independent wind and solar hybrid power system. Finally, a example analysis is used to show that the BFA has a strong global optimal capability and fast speed.