Abstract: Wind and solar energy have the characteristics of randomness and waviness.As the coordination among distributed generation（DG）,energy storages and loads is very complicated,proper combination of DG in an islanded microgrid is a primary problem for its reliability and economy.This paper used the bacterial foraging algorithm（BFA） to solve the optimal sizing problem of hybrid solar-wind DG in microgrid.The economic model of optimal sizing was built with the objective that takes annual costs of equipment,operation and maintenance,fuels,environment protection into account.The meteorological conditions of wind speed,solar radiation and temperature were input.According to alternatives of DG and power supply reliability,the types and optimal sizing of DG were designed.The results show the BFA has a strong global optimal capability and fast speed.This method can comprehensively evaluate the economy efficiency of DG and reduce redundant investment to satisfy customer’s diversification of reliability requirements according to meteorological conditions.