Modified Y molecular sieve

The invention discloses a modified Y molecular sieve, which is prepared by performing a primary exchange reaction on a NaY molecular sieve and rare earth solution, then introducing a phosphorus compound into an exchange serous fluid for further reaction, filtering and washing the mixture after the reaction, and roasting a filter cake under a vapor condition. The lattice constant of the modified Y molecular sieve is 2.450 to 2.479 nanometers, and the modified Y molecular sieve comprises the following components in percentage by weight: 2.0 to 6.0 percent of sodium oxide, 0.01 to 2.5 percent of phosphorus and 11 to 23 percent of rare earth oxide. Most of the rare earth of the modified molecular sieve is positioned in a sodalite cage of the Y molecular sieve, so the stability of the molecular sieve in a high-temperature hydrothermal environment is increased; and the structural acidity of the molecular sieve plays a good role in modulation. The modified Y molecular sieve used as an active component of a cracking catalyst has strong heavy oil conversion capacity and good coke selectivity.