The invention discloses a composite carrier and catalyst constituents by using the composite carrier, wherein the composite carrier is a solution formed by contacting magnesium halide with one or multiple electron donor compounds, by mixing the solution with silica sols whose average particle diameter is less than 30 um and spray drying, spherical particles can be obtained. When being used for olefin polymerization along with the catalyst promoter constituents in particular for propone polymerization, the catalyst constituents have shown high polymerization activity and stereospecificity.