The present invention relates to a method for removing residual alkali catalyst from biodiesel, characterized by the steps of: mixing choline chloride with a hydrogen bond donor to produce a deep eutectic solvent with a molar ratio of 1:1-3, wherein the hydrogen bond donor is selected from a group consisting of glycerol, ethylene glycol and 2,2,2-trifluoroacetamide; mixing the deep eutectic solvent with the biodiesel in counter-current to form a mixture, wherein the molar ratio of the deep eutectic solvent to the biodiesel is 0.75-3:1; settling the mixture to separate the biodiesel from the deep eutectic solvent; and collecting the biodiesel.