Abstract: Under certain selected experimental conditions, the authors study the whole process of thermal degradation of kerogens. Meanwhile, based on the evidence of DTG curves, the analyses of mixed degree of organic matter from different sources and the classification of kerogen types are carried out. With increasing temperature, the instantaneous reactions composing a DTG curve in releasing sequence of decomposed products can be taken to some extent as a modelling alteration profile of organic matter in geological bodies. Moreover, the weight lost in the whole process of thermal degradation of organic matter can be used to calculate the theoretical oil and gas productivities in various evolutional stages. It also can be used to assess oil/gas resources in combination with geological data.