A series of acrylic acid -sodium allyl sulfonate copolymers were synthesized via free radical polymerization. Acrylic acid and sodium allyl sulfonate were used as monomers, ammonium persulfate and sodium hypophosphite were chosen as complex initiation system. The change of slurry viscosity was studied under the different amount of ammonium persulfate, sodium hypophosphite and monomers. It was confirmed that 80℃ was the optimum reaction temperature. The adding amount of ammonium persulfate preferably was 0.9% by mass of monomer, and that of sodium hypophosphite was 3%. The ratio of monomer and initiator preferably was 24:1. The copolymers were characterized by Fourier Transform Infrared Spectroscopy (FTIR). The influences of polymers to viscosity, body strength and dispersion of clay slurry were measured. It was discovered that 0.25% AA-CLS brought the lowest slurry viscosity on 695mPa•s, which reduced from 1988mPa•s. The body strength was raised by 38%. And the best dispersion of the slurry was also obtained.