Provided is a Na—Y molecular sieve and a method for preparing the Na—Y molecular sieve, an H—Y molecular sieve and a method for preparing the H—Y molecular sieve, a hydrocracking catalyst, and a hydrocracking method. The average grain diameter of the Na—Y molecular sieve is 2-5 μm, and the sum of pore volumes of pores in 1-10 nm diameter accounts for 70-90% of the total pore volume of the Na—Y molecular sieve. The H—Y molecular sieve obtained from the large-grain Na—Y molecular sieve can be used as an acidic component in the hydrocracking catalyst. When the hydrocracking catalyst containing the H—Y molecular sieve is applied in the hydrocracking reaction of heavy oils that contain macromolecules, it can provide better cracking activity and product selectivity in the hydrocracking reaction.