The invention discloses a preparing method for urea resin modified by maize fermentation liquor and belongs to the field of urea resin preparation. According to the urea resin, after being peeled, washed, cooked and cooled, maize is fermented in an enzymolysis mode, then lemons are washed, sliced and fermented in an enzymolysis mode to extract citric acid, urea is added into maize fermentation liquor, formaldehyde is introduced, the citric acid is added for reaction, the amount of the adopted formaldehyde is slowly reduced until the maize fermentation liquor adapts to the formaldehyde, and then the mixture is mixed with sodium hydroxide and ammonium chloride, extruded, pelletized and dried to room temperature to prepare the urea resin. The method has the advantages that the formaldehyde emission content of the urea resin prepared by the method is low, the detected formaldehyde emission content is 0.06-0.1 mg/m<3>, and environmental pollution is small; the production process of the urea resin is simple, the storage stability is high, curing time is short, initial sticking quality is good, shrinkage is small, brittleness is small, water resistance is good, and the urea resin is not prone to aging.