A method of preparing a supported metallocene catalyst, including the steps of: preparing a silica carrier; loading an alkylaluminoxane on the inside and the surface of the silica carrier by bringing the silica carrier into contact with the alkylaluminoxane, a cocatalyst component; and sequentially loading one or more metallocene compounds on the silica carrier on which the alkylaluminoxane is loaded, wherein the alkylaluminoxane is dividedly loaded at different temperatures by a separate-input method, and wherein the silica carrier on which the alkylaluminoxane is loaded is obtained by the method of primarily loading 50 to 90 wt% of the whole input of the alkylaluminoxane on the silica carrier and carrying out the former reaction at 50 to 150°C, and secondarily loading the rest of the alkylaluminoxane on the silica carrier and carrying out the latter reaction at -10 to 40°C, wherein the method further includes the step of loading a borate compound as a second cocatalyst on the silica carrier on which the alkylaluminoxane and one or more metallocene compounds are loaded, wherein the supported metallocene catalyst is composed of: an outer layer including the area from each surface to a 1/3 position of the particle diameter toward the center and an inner layer including the rest of the area from the 1/3 position of the particle diameter to the center, in the cross-section of the supported catalyst particle, and includes the silica carrier on which the inside and surface thereof the alkylaluminoxane is loaded; and one or more metallocene compounds loaded on the silica carrier, and the content ratio (wt%) of Al/Si elements of the inner layer is 90 to 150 % or more compared to the content ratio (wt%) of Al/Si elements of the outer layer. preparing a silica carrier; loading an alkylaluminoxane on the inside and the surface of the silica carrier by bringing the silica carrier into contact with the alkylaluminoxane, a cocatalyst component; and sequentially loading one or more metallocene compounds on the silica carrier on which the alkylaluminoxane is loaded, wherein the alkylaluminoxane is dividedly loaded at different temperatures by a separate-input method, and wherein the silica carrier on which the alkylaluminoxane is loaded is obtained by the method of primarily loading 50 to 90 wt% of the whole input of the alkylaluminoxane on the silica carrier and carrying out the former reaction at 50 to 150°C, and secondarily loading the rest of the alkylaluminoxane on the silica carrier and carrying out the latter reaction at -10 to 40°C, wherein the method further includes the step of loading a borate compound as a second cocatalyst on the silica carrier on which the alkylaluminoxane and one or more metallocene compounds are loaded, wherein the supported metallocene catalyst is composed of: an outer layer including the area from each surface to a 1/3 position of the particle diameter toward the center and an inner layer including the rest of the area from the 1/3 position of the particle diameter to the center, in the cross-section of the supported catalyst particle, and includes the silica carrier on which the inside and surface thereof the alkylaluminoxane is loaded; and one or more metallocene compounds loaded on the silica carrier, and the content ratio (wt%) of Al/Si elements of the inner layer is 90 to 150 % or more compared to the content ratio (wt%) of Al/Si elements of the outer layer.