The invention discloses a polyurethane high-temperature-resistant anti-rutting modifier for road asphalt. The modifier comprises the following components in parts by the total weight of the modifier: 25-65 parts of one or two or more of diisocyanate, polyaryl polymethylene isocyanate and diisocyanate derivatives, 15-60 parts of one or two or more of polymer polyol and polymer polyamine, 2-15 parts of one or two or more of micromolecular polyol chain extender, micromolecular polyamine chain extender and micromolecular polyatomic acid chain extender, 0.01-3 parts of organic polyurethane catalyst, and 0-45 parts of poly-alkadiene polymer compound with a number-average molecular weight of 500-50000. The modifier can greatly improve the high-temperature resistance and anti-rutting properties of matrix asphalt and modified asphalt; and prepared modified asphalt is balanced in high and low-temperature performances, good in compatibility with matrix asphalt, and stored stably.