The invention discloses an optimized diesel hydrocracking catalyst and a preparation method thereof. The optimized diesel hydrocracking catalyst is prepared from the following raw materials in percentage by weight: 1 to 25 percent of a modified molecular sieve, 10 to 65 percent of gamma-Al2O3, 15 to 70 percent of amorphous silica-alumina, 9 to 40 percent of an adhesive and 10 to 35 percent of active metal oxide. The catalyst has a specific surface area of 200 to 400m<2>/g and a total pore volume of 0.30 to 0.65cm<3>/g. The catalyst is obtained by adding the modified molecular sieve into an inorganic aluminum salt solution for preparing the gamma-Al2O3, performing precipitation, drying and calcination to obtain a composite material of the molecular sieve and the gamma-Al2O3, and performing mixing, rolling, forming, drying and activating on the other materials and the composite material according to the material proportion of the catalyst. The molecular sieve in a catalyst carrier of the catalyst is high in silica-alumina ratio, high in dispersity in the carrier and large in specific surface area, so that the carrier has more uniform acidic sites; alumina makes contact with the molecular sieve more closely, so that the condensation point of a diesel distillate can be obviously reduced and the cetane number of diesel can be increased on the premise of ensuring high yield of the diesel.