Abstract: A Y-type molecular sieve and a preparation method therefor are provided. The grain size of the molecular sieve is 20-100 nm, preferably 40-70 nm, and more preferably 50-60 nm. The molar ratio of silica/alumina in the molecular sieve is 4.5-7, preferably 5.0-6.5, and more preferably 6.0-6.5. The proportion of 40-70 nm grains in the molecular sieve that is measured by means of a dynamic photoelectron scattering method is 80%-95%, and preferably 85%-93%. The Y-type molecular sieve has a small grain size, concentrated grain distribution, high silica-alumina ratio and good hydrothermal stability, and can meet the needs of industrial production.