The invention relates to a polyurethane complex film adhesive and a preparation method thereof. The polyurethane complex film adhesive comprises a solidifying agent A component and a main agent B component, wherein the solidifying agent A component is an isocyanate-terminated prepolymer obtained by reacting polyisocyanate with polyalcohol a; the main agent B component is a polyhydroxylated compound prepared by reacting special polyalcohol, epoxy resin and polyalcohol b with polyisocyanate; the mole ratio of the functional groups of the A and B components is NCO:OH=(1.0-2.0):1. The process for preparing the polyurethane complex film adhesive is simple; the prepared product has the advantages of high initial viscosity, good wetting property on a base material, good hydrolysis resistant stability, wetness and heat resistance, long opening time, good compatibility, high adhesive force on metals, chemical resistance, good compound flexible package appearance and high stripping strength, can be used for series complex films with generality, high solid content, solvent-less lamination, and the like and overcomes the defects of low solid content, poor wetness, poor hydrolysis resistance, no wetness and heat resistance, short opening period, poor composite adhesive force on the metals, and the like of a common polyurethane complex film adhesive.