Abstract: In this paper, the occurrence of steranes and their thermal evolutionary patterns are approached based on the results of thermal-modelling experiments. Different steranes have different occurrence. Regular steranes, rearranged steranes and 4-methyl steranes mainly come from the transition of non kerogen precursors, and the degradation of kerogcn do not generate these compounds basically. However, pregnanes are mostly generated by the degradation of kerogen. All eight parameters most in use, such as aaa(20R)C₂₇,C₂₈,C₂₉% +aa),have multiple solutions. The higher the value of aaa(20R)C₂₉% and the lower the value of the other parameters, the more accurately the parameters indicate the maturity (iow-mature to mature). Otherwise, they have not any indicative significance.