A hydrocracking catalyst carrier and a preparing method thereof are disclosed. The hydrocracking catalyst carrier comprises a beta molecular sieve, amorphous silicon aluminum and aluminum oxide, wherein properties of the beta molecular sieve are as follows: the specific surface area is 400-800 m2/g, the total pore volume is 0.4-0.55 mL/g, the SiO2/Al2O3 mole ratio is 30-60, the relative crystallinity is 120-140%, the infrared acid content is 0.55-1.0 mmol/g, the non-framework aluminum accounts for less than 1% of the total aluminum, the amount of medium-strong acids which is measured by a NH3-TPD method accounts for 70-85% of the total acid amount, and the percent of Na2O is not more than 0.15 wt%. The preparing method includes mixing the beta molecular sieve, the amorphous silicon aluminum and the aluminum oxide, kneading and forming to prepare the carrier. The beta molecular sieve which is proper in silicon aluminum ratio, large in specific surface area, proper in acidity, reasonable in pore structure and low in content of non-framework aluminum, and the amorphous silicon aluminum are adopted as cracking components of the hydrocracking catalyst carrier. A prepared catalyst is characterized by producing a clean diesel oil product with a low condensation point with the highest yield, improving properties of hydrogenation tail oil, and the like.