The invention discloses a binder for a hot melt adhesive film as well as a preparation method of the binder and an application of the binder in an FFC wire. The binder comprises the following components in percentages by mass: 19%-21% of saturated polyester resin A, 10%-19% of saturated polyester resin B, 6%-9% of saturated polyester resin C, 38%-43% of a flame retardant, 5%-7% of a hexamethylenediisocyanate curing agent A, 1%-3% of a 2,4-diphenylmethane diisocyanate curing agent B, 1%-3% of an isophorone diisocyanate curing agent C and the balance of a filler; and the binder is prepared by simple three steps and used as the hot melt adhesive film of the FFC wire, and the hot melt adhesive film has a PET hot melt adhesive film layer of 19-50 [mu]m, a pre-coating layer of 1-3 [mu]m and a high-heat-resistant adhesive layer of 20-50 [mu]m in sequence from the top to the bottom. The hot melt adhesive film disclosed by the invention has excellent high-temperature-resistant high-humidity-resistant stability and heat-shock-resistant stability.