The invention discloses an anti-aging modified asphalt and a preparation method thereof. The modified asphalt comprises, by weight, 0.5-5 parts of an organic-inorganic composite material, 0.2-3.0 parts of a hindered phenol antioxidant and 0.1-2.0 parts of a phosphite antioxidant, wherein the organic-inorganic composite material is formed through co-hydrolysis and polycondensation reactions of ethyl orthosilicate and organosilane. The anti-aging performance of the modified asphalt is greatly improved, and the asphalt has a high 60 DEG C viscosity and a very high low-temperature ductility, so ruts in summer and frost cracks in winter are avoided.