Abstract: A flow apparatus for measuring heat of vaporization of liquids under pressure up to 6 MPa,and temperature from 260 K to 480 K is developed.Heats of vaporization of water are measured,and the differences of our experimental results with literature values are within 0.85%.The heats of vaporization HFC134a and HFC125 used as the alternatives of refrigerant Freon are determined, and 14 values of heat of vaporization are reported in this paper.