The invention discloses a method for preparing a light-fast waterborne polyurethane coating material. The method comprises the steps: mixing polytetrahydrofuran ether glycol and isophorone diisocyanate in the presence of a dibutyltin dilaurate catalyst, reacting for 1-4 hours at the temperature of 80-100 DEG C, adding liposome and coroxon, and reacting for 2 hours at the temperature of 90 DEG C, so as to obtain a polyurethane prepolymer A; adding a chain extender, 1,4-dioxane and riboflavin sodium phosphate into the prepolymer A, reacting for 1.5-3.5 hours at the temperature of 65-85 DEG C, adding a mixed solution A, reacting for 1-2 hours at the temperature of 75-85 DEG C, adding triethylamine to carry out neutralization reaction for 30-50 minutes, and adding water to emulsify, thereby obtaining the light-fast waterborne polyurethane coating material. The prepared light-fast polyurethane coating material is environment-friendly and cheap, is widely applied to the surfaces of walls, furniture and metallic utensils and serves as a binder of plastics, glass, paper making and textiles.