Abstract: Organic heat transfer fluid has been applied for heating system in various industries. Thermal stability is an important performance, which is an indication of decomposition and polymerization of oil at high temperature. SH/T 0680-1999《Heat Transfer Fluids-Determination of thermal Stability》was revised, taking standard DIN 51528-1998《Unused Heat Transfer Fluids-Determination of thermal Stability》as a reference. The differences are that the revised method requires to use capillary chromatographic column in gas chromatograph analysis, report the boiling range of sample before end point of 538℃, uniform the temperature distribution in whole equipment, and change the test time. The standard revised can reflect better thermal stability of different kinds of organic heat transfer fluids at different temperature and different heating time.