This article introduced how to use solid base CaO which exists in the subcritical methanol phase to catalytic the transesterification of hogwash fat to synthesis the biodiesel, The effects of biodiesel synthesis such as: the reaction temperature, the molar ratio of alcohol to oil, the dosage of catalyst and the reaction time were been studied.The result shows that the concentration of fatty acid methyl ester in the products of catalytic hogwash oil transesterification may reach to 89.2% under the conditions that the tempreture 140℃, molar ratio of methanol to oil 12:1,the amount of catalytic 1.2% and the reaction time 30min.