The superabsorbent poly(AM-SAS-AA)s were synthesized to improve the water absorption capacities in comparison with the poly(AM-SAS) by an aqueous solution polymerization method from acrylamide (AM), sodium allylsulfonate (SAS), and acrylic acid (AA). The reaction conditions were controlled by varying the AA concentrations and fixing other agent concentrations to obtain the optimal superabsorbent poly(AM-SAS-AA). The poly(AM-SAS-AA) showed maximal absorption capacity at 0.3 mol/L among AA concentrations from 0.053 mol/L to 0.4 mol/L. The water absorption capacities of poly(AM-SAS-AA)s prepared at the optimal reaction condition were measured within the temperature ranges from 298.15 K to 318.15 K. Those experimental dan were used to describe the effect factors on absorption capacities and swelling equilibria data among those data were correlated with the swelling models to estimate the interchange energy parameters. Each swelling models combined with group contribution models (UNIFAC, ASOG) was introduced to calculate the swelling equilibria of water(1)/poly(AM-SAS-AA)(2) systems. The swelling behaviors could be described by the estimated parameters, and the calculated values agreed well with the experimental data.