The influences of the bathing solution and crosslink density on the swelling equilibrium of ionic thermo-sensitive hydrogels due to temperature stimulus are studied by mathematical modeling. The model used is termed the multi-effect-coupling thermal-stimulus (MECtherm) model with consideration of multiphases and multiphysics. It is used for the steady-state numerical simulation of the hydrogels in swelling equilibrium after it is verified well by comparison with available experimental data concerning the variation of volume swelling ratio with temperature. The phenomenon of volume phase transition is simulated for the thermal-stimulus responsive hydrogel. Simulations predict well the influences of the bathing solution concentration and crosslink density of polymeric network on the swelling equilibrium of the hydrogels.