The invention relates to a supported late transition metal catalyst for ethylene polymerization, and a preparation method thereof, the catalyst comprising (a) a late transition metal compound; (b) hydrocarbyl silicon chloride; (c) an organoaluminum compound; (d) magnesium chloride A reaction product of a carrier; the preparation method thereof comprises: (1) preparation of a chlorinated hydrocarbyl silicon-modified magnesium chloride carrier, (2) preparation of an organoaluminum-modified magnesium chloride carrier, (3) preparation of a transition metal catalyst supported by magnesium chloride, and the obtained The late transition metal catalysts catalyzed ethylene polymerization or copolymerization have high polymerization activity. The preparation method of the magnesium chloride carrier used is simple, and the obtained loaded catalyst particle has good shape and adjustable size. The supported catalyst obtained by the method catalyzes the copolymerization reaction of ethylene and α-olefin, has high polymerization activity, and the obtained resin powder has good particle shape and high bulk density, and is applicable to slurry method and gas phase method polymerization technology.