The invention belongs to the field of road engineering, and particularly relates to a hyperviscous and high-elastic asphalt modifier applicable to steel bridge deck pavement. The asphalt modifier comprises the following raw materials in parts by weight: 3-10 parts of junked tire rubber powder, 3-10 parts of polyethylene wastes, 3-8 parts of styrene-butadiene-styrene block copolymer, 1-5 parts of styrene-isoprene-styrene block copolymer, 1-5 parts of terpene resin, 5-10 parts of solvent naphtha, and 0.3-0.7 part of alcohol ether carboxylate adhesion agent. In addition, a modified asphalt and amodified asphalt mixture are prepared on the basis of the modifier, the 60 DEG C dynamic viscosity of the modified asphalt prepared by applying the modifier can reach more than 300000Pa.s, and the performance grading reaches PG 88-28; and the asphalt mixture has favorable water stability, higher dynamic modulus, higher track dynamic stability and low temperature failure strain, and can resist complicated mechanics and temperature environment of a steel bridge deck.