The present invention discloses 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 2~5μm, and the sum of pore volumes of pores in 1-10nm 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.