Abstract: Characteristics of thermal evolution with in creasing depth of organic matter in different sedimentary basins of Meso-Cenozoicage in China are reviewed on the basis of analytical data of soluble saturated hydrocarbons, asphaltenes and insoluble kerogen etc. from source rocks. Six stages are proposed for the whole process of evolution, and the structural changes of organic matter for each stage are studied with data obtained form analysis of elements, infrared spectrum, chromatogram, chromatogram-mass spectrogram and paramagnetie resonanceetc., leading to the further inquiry of the mechanism and process of oil and gas generation.