The invention discloses a hydrocracking catalyst and a preparation method thereof. The hydrocracking catalyst contains a compound of amorphous silica-alumina and a Y-type molecular sieve. In NaY molecular sieve modification, before final hydrothermal treatment, amorphous silica-alumina slurry and a surfactant are introduced so that the compound is obtained. Therefore, molecular sieve and amorphous silica-alumina dispersion is uniform and molecular sieve agglomeration or channel blocking is avoided so that specific surface areas and pore volumes of a carrier and the hydrocracking catalyst are greatly improved. The preparation method reduces a strong acid amount and improves a moderately strong acid ratio and a B acid amount in case of the little change of a total acid amount, reduces excessive cracking, avoids secondary cracking, is conducive to improvement of middle distillate selectivity, and reduces a yield of low-additional value products such as dry gas, liquefied gas and light naphtha.