The present invention provides a catalyst component for ethylene polymerization, a process for preparing the same, a catalyst comprising the same, and a process for polymerizing ethylene using the catalyst. The catalyst component comprises a reaction product, supported on an inorganic oxide support, of a magnesium complex, a titanium compound, an alcohol compound, and an organoaluminum compound, wherein said magnesium complex is formed by dissolving a magnesium halide in a solvent system comprising an organic epoxy compound and an organo phosphorus compound. The catalyst according to the invention is especially suitable for slurry phase polymerization of ethylene. The catalyst according to the present invention has high catalytic activity, and a good hydrogen response, with the resultant polymer having a more uniform particle size diameter and a narrow particle size distribution.