This paper introduces the research on how to improve the measuring accuracy of "sting the thermal performance of refrigerant compressor. Some new design methods which have been adopted for the refrigerant system and apparatus are presental and the application of new technique and fop control theory in the development of a fully automatic calorimeter is described. The experimental device built accordinglyhas the feature of stabilizing quickly the working condition of the tested compressor and its measuring accuracy is within 1.5%.