The invention discloses an alumina-modified silica gel supported catalyst, and a preparation method and application thereof. The catalyst comprises a catalyst active component and alumina-modified silica gel, wherein the catalyst active component is prepared by reacting metal salt, zinc alkyls, hydroxy-containing compound and solvent. The preparation method is implemented by evenly mixing the catalyst active component, the solvent and the alumina modified silica gel in a nitrogen atmosphere. The catalytic activity of the catalyst is enhanced by 10-150% as compared with the activity of the independently used non-supported tricomponent catalyst for catalyzing CO2/epoxy propane copolymerization. The number-average molecular weight of the polymer is greater than 0.1 million, the weight-average molecular weight is greater than 0.4 million, and the content of carbon dioxide-epoxide alternating structure (carbonate) is higher than 95%.