The invention discloses a star-shaped polymer papermaking dispersant and a preparation method thereof. The dispersant is prepared through copolymerization among the following raw materials in percentage by weight: 30 to 35% of acrylamide monomer, 15 to 25% of sodium acrylate monomer, 1 to 4% of acrylonitrile monomer, 3 to 4% of methyl acrylamide monomer, 6 to 7% of 2-ammonium acrylate-2-methylpropane sulfonate monomer, and the balance being distilled water. The five monomers can form a polymer having a straight chain structure with branch chains through co-polymerization. Introduction of AMPS can accelerate the dissolution speed of the polymer, and shorten the dissolution time from 60-90 minutes to 40-60 minutes. AAM and AMPS both have branch groups, and thus the polymer can fully contact with the paper pulp fibers. The tails of the molecules tangle and combine with each other to form sheet-shaped macromolecules. After the polymer is mixed with paper pulp fibers, the free side chains of the polymer will effectively catch the fibers, the fibers are orderly arranged, and thus the fibers are effectively dispersed.