The critical points of CO 2-H 2O, NaCl-H 2O and CO 2-NaCl-H 2O fluid mixtures were measured by observing the disappearance and reappearance of the meniscus by using the visible-type autoclave. The critical points of CO 2-H 2O and NaCl-H 2O fluids shift linearly with the variation in ion concentrations. The general tendency of the critical point shifting of H 2O-NaCl- CO 2 multi-component fluid was similar to the H 2O-CO 2 fluid. However at higher NaCl concentrations, the variation in the critical point was higher for higher CO 2 concentrations. This phenomenon is believed to be due to the interaction of ion or ions with water molecules in the fluid.