The embodiment of the invention discloses a modifier as well as a preparation method and application thereof. The modifier is prepared from the following raw materials in parts by weight: 40-80 partsof thermoplastic elastomer polymer, 10-30 parts of modified petroleum resin, 5-20 parts of thermally sensitive resin, 1-5 parts of a stabilizer, 5-20 parts of a plasticizer and 1-3 parts of an antioxidant. The thermoplastic elastomer polymer in the embodiment of the invention has an effect of enhancing and toughening the modifier, so that the high/low-temperature service performance of the modifier can be ensured; the modified petroleum resin has strongly polar groups and is matched with the thermoplastic elastomer polymer, so that the viscosity of asphalt at a service temperature can be obviously improved, and the pavement performance of the mixture is ensured; the thermally sensitive resin has the characteristic of excellent temperature sensitivity and is matched with the plasticizer andthe stabilizer, so that the applicable viscosity of the asphalt at a high temperature can be effectively reduced, and the construction workability of the mixture is improved; and moreover, since thehigh temperature viscosity is reduced, the melting dispersion characteristic of the modifier can be improved.