Objective Alumina were graft modified to improve their dispersion stability in the aqueous slurry. Methods Alumina were firstly modified with KH570 (γ-methacryloxypropyltrimethoxysilane), then polyacrylamide was grafted onto the silanized alumina by radical grafting polymerization. The modified alumina (Al2O3-g-PAM) were characterized by IR and SEM. The influence of some important parameters, such as the adding methods of feeds， reaction temperature and the monomer concentrations, on the grafting ratio were thoroughly studied． Results The optimal conditions of alumina modification: reaction temperature was 80℃, concentration of monomer was 0.5 mol/L and monomer was fed 20 min after adding initiator. The dispersion stability of the modified alumina in water and in aqueous slurry was obviously improved. The grafting ratio of alumina was closely related to the dispersion stability both in water and in aqueous slurry. The higher the grafting ratio, the better the dispersion stability in water was. However, only when the grafting ratio was in a certain range, alumina could have good dispersion stability in aqueous slurry. Conclusion The key parameter of the dispersion stability was the regulation of grafting ratio of alumina. The modified alumina could have proper dispersion stability in aqueous slurry when the grafting ratio was regulated in the range of 2%~3%.