In this article, we successfully designed and fabricated polyacrylate/poly(ethylene glycol) interpenetrating network (PAC/PEG IPN) hydrogel by a two-step technique. The influences of synthesis parameters, such as crosslinker dosage and neutralization degree of PAC, on the equilibrium swelling ratio (SR) of the PAC/PEG IPN hydrogel were investigated. Based on Flory theory, a simplified experiential formula Q(H2O)(5/3) = 14.72I(-1) + 207.43 was proposed. The results revealed that the theoretical SR of the PAC/PEG IPN hydrogel was consistent with experimental value in the presence of univalent salt solution. In this case, the SR of the hydrogel can be calculated without measurement. While for multivalent salt solutions, the theoretical and experimental results are inconsistent owing to chelations between carboxylic and carboxylate groups of the PAC/PEG hydrogels and the cations in the solution.