A high-temperature and high-pressure optical cell VLE apparatus has been applied to measure phase equilibrium properties of n-tetradecane in the supercritical binary solvent (0.367propane+0.633 nbutane mass fraction) at temperatures of 413.15 K, 433.15 K, and 453.15 K between of pressures (0.9 and 6.6) MPa. The combined expanded uncertainty of the temperature, pressure, and concentration measurements at 0.95 confidence level with a coverage factor of k = 2 is estimated to be 0.15 K, 0.0022, and 0.035, respectively. The critical parameters (TC, PC, C w ) were determined based on the measured isothermal phase equilibrium data of the ternary system n-tetradecane+ propane/n-butane. It is shown that the critical temperature and pressure of the n-tetradecane+ propane/n-butane system increases with concentration of n-tetradecane increases.