Acrylic acid-itaconic acid copolymers were synthesized in water. Ammonium persulfate was used as initiator and sodium hypophosphite as chain transfer agent. The influence of different reaction conditions on the clay slurry viscosity was investigated. The optimal conditions were shown as follow: the temperature was 80℃, 0.8% ammonium persulfate by the mass of monomer, 9% sodium hypophosphite, and 0.9% initiator. The structure of copolymer was characterized by FTIR. The viscosity and bending strength of the slurry and the microstructure of the fracture surface were also studied. The results showed when adding 0.25% copolymer, the viscosity of the clay slurry was reduced from 1998mPa•s to 690mPa•s and the body strength was increased from 1.96MPa to 2.88MPa.