The invention relates to a preparation method of an elastic polyurethane gel coat for the outside of a film of a wind blade. The method mainly comprises the following steps of: firstly, respectively adding resin capable of reacting with -NCO, rutile titanium white powder, inorganic filler, a weather-resistant assistant, an antistaining agent, a nano additive, a dispersing agent, a defoaming agent, a rheological additive, an anti-sedimentation agent and a flatting agent into a stirring tank in sequence, and dispersing and grinding to below 50 micrometers; then adjusting the viscosity by using an environment-friendly organic solvent, and then adjusting the color by using color paste; and finally, mixing two kinds of polyurethane curing agents, and reacting the two polyurethane curing agents with raw materials sufficiently, and diluting by using the environment-friendly organic solvent to 60-90%. The invention has the beneficial effects that the elastic polyurethane gel coat has excellent wind and sand resistance and rain erosion resistance as well as wide application range; and the stretch rate of the polyurethane gel coat can be increased to over 50%, and the elastic polyurethane gel coat has favorable weather resistance and excellent elasticity at low temperature.