The invention discloses a modified polymer. The polymer is one of hydroxyl-terminated hydrogenated poly-1,3-butadiene. Meanwhile, the invention discloses a preparation method of the modified polymer; in a preparation process, the hardness and flexibility of the modified polymer can be adjusted through adjusting conditions of an addition reaction and a ratio of an addition way. The invention further discloses an EVA (Ethylene-Vinyl Acetate copolymer) shoe material treatment agent containing the modified polymer; the treatment agent realizes similarity and intermiscibility with an EVA main chain structure through utilizing low polarity of the modified polymer; meanwhile, an amine ester structure formed by a reaction of hydroxyl and isocyanate realizes effective adhesion with a polyurethane adhesive; the dosage of chlorinated polypropylene is reduced, so that the modified polymer has a wide application range and a good adhesion effect, has a good anti-yellowing performance and good affinity permeability on materials and can realize non-roughing utilization of a shoe material.