The performance of supercritical fluid (SCF) as a solvent can be greatly affected by addition of an entrainer to the system. In this study, a constant volume visual method is used to measure the critical point of CO2+n-butyraldehyde, CO2+ i-butyraldehyde and CO2+alcohol binary systems and CO2+entrainer+trisodium salt of tri-(m-sulfonphenyl)phosphine (TPPTS) ternary systems, which provides us good theoretical basis for supercritical extraction and chemical reaction. The relationship between critical point and concentration of the entrainer are discussed. The phase behavior of binary system and that of ternary system are compared. The relationship between the concentration of TPPTS and critical point of binary systems are also discussed.