Abstract: The present invention relates to a supported polyolefin catalyst and its preparation and application. Its main catalyst is composed of a support and a transition metal halide; the support is composed of a magnesium halide compound, a silicon halide compound, an alcohol compound having 5 carbon atoms or less, an alcohol compound having carbon atom number of 6-20 in a molar ratio of 1:(0.1 to 20):(0.1 to 5):(0.01 to 10); the molar ratio of the magnesium halide compound and the transition metal halide is 1:(0.1 to 30); during the preparation process of the main catalyst, an organic alcohol ether compound is added, the mass ratio of the magnesium halide compound and the organic alcohol ether compound is 100:(0.1 to 20); and the molar ratio of the transition metal halide in the main catalyst and the co-catalyst is 1:(30 to 500).