The invention discloses a hydrated alumina composition and a preparation method thereof, and a molding body, a preparation method and applications thereof. The hydrated alumina composition contains hydrated alumina, a BETA molecular sieve and a compound having at least two proton acceptor sites, wherein the [phi] value of the composition is less than 5. The present invention further discloses a catalyst using a molding body formed from the hydrated alumina composition as a carrier and having hydrogenation catalysis effect, and a preparation method thereof, and a hydrocracking method. Accordingto the present invention, the high-strength molding body is prepared by using the hydrated alumina wet gel as the starting raw material, such that the hydrated alumina wet gel drying step is eliminated, the total process is simplified, the total operation energy consumption is reduced, the dust pollution caused by the application of the pseudoboehmite dry glue powder as the raw material is avoided, and the working environment is greatly improved; and the catalyst using the molding body prepared from the hydrated alumina composition as the carrier has high catalytic activity in the hydrocracking of hydrocarbon oils.