The influence of inorganic ions on the molecular size of hydrophobically associating polymer S308 was investigated by light scattering technology. The dependence of the molecular size on polymer concentration and salt content was also studied. Meanwhile, we also tested the rheological properties of S308 in salt solvent. The results showed the Rh of the S308 solutions prepared by NaCl、KCl、NH₄Cl solutions with the concentration of 1 mol/L and CaCl₂ solution with the concentiaon of 0.01 mol/L, respectively, was arranged as follows, R_h（Ca²⁺）< R_h（K⁺）≈ R_h（NH⁴⁺）< R_h（Na⁺）. In other words, the order of the influencing capacity of these cations was as follows, Ca²⁺>K⁺≈NH⁴⁺>Na⁺. When the Na⁺h of the polymer in the NaCl、Na₂CO₃ and Na₂SO₄ solutions was of 217 nm, 277 nm and 238 nm, respectively, indicating that polymer molecular size tended to be larger in solvent containing high valence anions than in solvent containing monovalent anions when the solvent contained the same kind and amount of cations. In different salt solvents, the apparent viscosity of the polymer solution basically increased with the increase of the molecular size. Besides, with the salt content increasing, the molecular size of S308 increased at first and then went down, and the ratio of gyration radius to the hydrodynamic radius (R_g/R_h) decreased gradually, indicating the polymer chain transformed from stretch to curl.