This invention relates to a method for converting animal and vegetable oils into fatty acid monoesters without discharge. The method comprises: pumping animal and vegetable oils, monohydric alcohols and catalyst into a pressure reaction tank, sealing, stirring, heating to the transesterification temperature, performing transesterification reaction, spraying the reaction mixture into an evaporator, evaporating excess monohydric alcohols and catalyst, introducing into a condenser, condensing into liquids, recovering, and demixing the mother liquid after monohydric alcohols and catalyst are evaporated to obtain fatty acid monoesters (low specific gravity) and glycerol byproduct (high specific gravity). The method has such advantages as abundant raw materials, easy recovery of catalyst, mild production conditions, short reaction time, and simple process, and is suitable for industrialization.