The invention relates to the field of mesoporous materials, and discloses a spherical porous mesoporous composite material and a supported catalyst and a preparation method thereof. The spherical porous mesoporous composite material comprises a mesoporous molecular sieve material with a one-dimensional straight-through pore structure and a mesoporous molecular sieve material with a hexagonal porestructure, and the spherical porous mesoporous composite material has an average particle size of 21 to 29 microns, a specific surface area of 200-650 m<2>/g, and a pore volume of 0.5-1.8 ml/g, and the pore diameter is in trimodal distribution. The spherical porous mesoporous composite material provided by the invention has the advantages of stable mesoporous structure and uniform particle size distribution, the spherical porous mesoporous composite material as a catalyst carrier is high in strength and not easily broken, and the supported polyethylene catalyst prepared from the spherical porous mesoporous composite material has high catalytic activity when catalyzing ethylene polymerization. A polyethylene product which has a low bulk density and a low melt index and is not easily brokencan be obtained.