Abstract: Biodiesel fuel, chemically consisted of fatty acid methylester (FAME) produced by methanolysis of natural triglycerides such as animal fats and vegetable oils, is a kind of biomass energy. KF/CaO was used as solid base catalyst for transesterification to produce biodiesel fuel with ultrasound as an auxiliary means. Compared with mechanical stirring, ultrasound treatment is an effective method to increase the yield of biodiesel and shorten the reaction time. By single factor method, the optimization of reaction conditions has been studied with ultrasound. The results show that the reaction conditions are as following. The weight ratio of catalyst to oil is 3%, and molar ratio of methanol to oil is 12. The sound frequency is 20kHz with intensity of 1.01W/cm². Under the above conditions, the yield of biodiesl reaches 99.6% at 65℃ in 1h.