A new expression of mixing rule is suggested according to the Mayson′s mixing rule in this paper, which adopts the Redlich Kwong cubic equation of state and the modified Chueh Prausnitz method to calculate the experiment critical points of six binary mixtures CO 2+toluene, CO 2+cyclohexane, CO 2+ n butanal, CO 2+ i butanal , CO 2+methanol, CO 2+ethanol. The coefficients of interaction parameter in the expression of mixing rule were optimized from experimental data. The calculated results of critical temperature and critical pressure meet the experiment data well. The maximum relative errors of temperature and pressure between the calculation results and experiment data are 1 493% and 5 2236% respectively, indicating that the proposed expression of mixing rule is reasonable. This may provide a fundamental method for studying and predicting the properties of supercritical fluids. A new expression of mixing rule is suggested according to the Mayson’s mixing rule in this paper, which adopts the Redlich Kwong cubic equation of state and the modified Chueh Prausnitz method to calculate the experiment critical points of six binary mixtures CO 2 + toluene, CO 2 + cyclohexane, CO 2+ n butanal, CO 2+ i butanal, CO 2 + methanol, CO 2 + ethanol. The coefficients of interaction parameter in the expression of mixing rules were optimized from experimental data. The calculated results of critical temperature and critical pressure meet the experiment data well. The maximum relative errors of temperature and pressure between the calculation results and experiment data are 1 493% and 5 2236% respectively, indicating that the proposed expression of mixing rule is reasonable. This may provide a fundamental method for studying and predicting the properties of supercritical fluids.