As an important technique to study the characteristic of thermal reactions, thermogravimetric mass spectrometry analysis could explore matter transform and dynamic procedure of thermal reactions in which for most cases the information comes from overall reactions. Therefore disassembling the elementary reactions, by different experimental method on the basis of reaction mechanism, was the key factor in fundamental theory of thermal analysis. A novel perspective and method were provided with research of dolomite powder, depending on a series of experiments varying the partial pressure of CO2, to parse two elementary reactions. Furthermore, theoretical calculation result was obtained from evolved gas by means of the recognized method-equivalent characteristic spectrum analysis (ECSA).