Abstract: The reliability of natural bitumen reflectance (R_OB) as a maturity index of carbonate strata is always a controversial issue which has not been settled completely.It is revealed in studies that bitumen of different genetic type possesses different optical evolutionary characteristics and rules and has characteristic molecular structural and chemical composition.Therefore,special relational equations between R_OB and vitrinite reflectance (R^O) must be set up respectively for different bitumen,and the geneses of bitumen be classified according to the characteristic structure and composition of different bitumen types.Besides,the evolutionary characteristics of aromatic fraction and asphaltene in bitumen are studied preliminary by means of Gas Chromatography/ Fourier Transform Infrared Spectroscopy (GC/FTIR) and High-performance Liquid Chromatography (HPLC) There are indeed a wealth of evolutionary information in these compounds.But the studies on them is seriously behindhand.