The invention relates to the field of polyurethane and particularly relates to a method for preparing a photo-crosslinking polyurethane film. The method comprises the following steps: adding 24.5g of isophorone diisocyanate and 4 droplets of catalyst into a 250ml four-mouthed bottle, adding 57.1g of polyether polyol into a dropping funnel, carrying out dropwise adding, carrying out a reaction for 1 to 1.5 hours while controlling the temperature to 40 DEG C to 50 DEG C, measuring NCO content by a di-n-butylamine method, adding 3.75g of 2,2-bishydroxymethyl propionate after the NCO content meets requirements, carrying out a reaction for 2 to 3 hours at the reaction temperature of 60 DEG C to 70 DEG C, dropwise adding 3.47g of hydroxyl-2-ethyl methacrylate and a polymerization inhibitor when the NCO content is approximate to a theoretical value, heating the temperature to 70 DEG C, carrying out a reaction for 3 to 4 hours, carrying out sampling, carrying out infrared detection, and obtaining a polyurethane prepolymer when characteristic peaks of an NCO group disappear; loading the prepolymer into a four-mouthed flask, adding triethylamine into the four-mouthed flask according to the mole ratio of 1: 1 in a dropwise adding manner, and carrying out a neutralization reaction for 0.5 to 1 hour at the temperature of 50 DEG C, thereby obtaining a composite nano-emulsion. According to the method, the operation is simple, the operation is convenient, the comprehensive performance of the product is good, and the method is efficient, energy-saving, environmentally friendly, safe and sanitary.