The surface tension of oil/refrigerant mixture was measured at pressurized condition. The density of the PAG/CO2 mixture shows little change with CO2 concentration. The surface tension of the PAG/CO2 mixture sharply decreases with CO2 dissolution. The correlation equation of the surface tension of the PAG/CO2 mixture was proposed. The surface tension of the mixture at 100 °C and 10 MPa is estimated at 14.6 mN m−1.