The present invention relates to a technical field of CMP pad manufacture, and more particularly to a CMP layer based on porous cerium oxide and a preparation method thereof. The CMP layer of the present invention is formed by mixing and curing a polyurethane prepolymer, a crosslinking agent and the porous cerium oxide, including steps of preheating the polyurethane prepolymer under vacuum, then adding a porous cerium oxide filler to the polyurethane prepolymer, and thoroughly mixing to obtain a mixed prepolymer; moving the mixed prepolymer to a first tank, and performing heat preservation, stirring, and circulation treatments; adding the crosslinking agent to a second tank and performing a melting treatment; correcting an injection weight ratio of the first tank and the second tank, then rapidly mixing, so as to inject into the mold; and then curing and vulcanizing to obtain the polishing layer.