Abstract: The degradation of biochemical active mass especially curative compositions, during the traditional processing of Chinese herb has become an increasingly serious problem while the development and utilization of Chinese herb becomes more comprehensive. Based on the introduction to the principle and the technical points of vacuum freeze drying in Chinese herb processing, the degradation in the drying process of Chinese herb was analyzed through the measurement of catolpol content in Rehmannia by means of High Performance Liquid Chromatography. The reaction order, rate constant and the coefficient of the prospective quality control model were determined and verified by experiment. It is indicated that the method of vacuum freeze drying can effectively prevent the degradation during the traditional drying process of Chinese herb, and the quality control model developed in this paper can reflect the effects of moisture content, drying time and temperature on the degradation of curative compositions.