Abstract: The effect of inorganic cations on the features of agglomeration solution is very important during the process of chemical agglomeration. Molecular dynamics simulation method was used to study mechanism of Na+, Mg²⁺ and Ca²⁺ on the properties of partially hydrolyzed hydrophobically modified polyacrylamide（HMHPAM） solution. The capacity of water absorption and viscosity of HMHPAM solution were analyzed by the characterization methods of radius of gyration and radial distribution function. Result of radius calculation clearly showed that the viscosity of HMHPAM solution was reduced by the addition of cations and the influence level of cations on HMHPAM solution was Ca²⁺ ＞ Mg²⁺ ＞ Na+. The results of cation hydration showed that the hydrated radius of Mg²⁺ was the smallest, its capacity of water absorption was the strongest and so the water solubility of HMHPAM was greatly affected by Mg²⁺. The results of radial distribution function showed that Ca²⁺ could enter the first hydration shell of acrylic anions and interact with acrylic anions directly. It plays a strong effect on electrical shielding. So Ca²⁺ has the greatest impact on the viscosity of the HMHPAM solution. While the influence of Na+ on HMHPAM solution is minimal, it can only play a weak effect on electrical shielding.