The invention discloses modified asphalt and a preparation method thereof. The modified asphalt disclosed by the invention is prepared from the following raw material components in parts by weight: 100 parts of catalytic slurry oil, 60 to 100 parts of residual oil, 3 to 10 parts of a delay agent, 0.1 to 1 part of an oxidant and 3 to 10 parts of a chemical modifier, wherein the chemical modifier isa methanesulfonic acid solution of phosphorus pentoxide. According to the modified asphalt and the preparation method thereof, the catalytic slurry oil can be directly used as a production raw material of asphalt, and procedures such as atmosphere-vacuum distillation or solvent deasphalting and the like do not need to be carried out on the catalytic slurry oil; after the catalytic slurry oil is blended and modified, the modified asphalt for roads is manufactured; therefore, the production process is greatly simplified, and the production cost is reduced.