Abstract: The hyperbranched unsaturated polymer monomer was synthesized using maleic anhydride and diethanolamine as starting materials. This monomer was then polymerized with acrylic acid and diallyl dimethyl ammonium chloride, by using ammonium persulfate as initiators to produce a paper strengthening agent. It was found that the polymerization performing at the molar ratio of 2:1:1 of the hyperbranched unsaturated polymer monomer, acrylic acid and diallyl dimethyl ammonium chloride, 3% weight content of ammonium persulfate, temperature ranging from 80-85℃, and reaction time for 3 h, can achieve 98.6% monomer conversion. The polymer had relative molecular mass of 51 300.