Choosing samples of qualitymarine source rocks in various strata in South China，we make a study of mineral composition，correlation between organic matter and mineral composition，occurrences of organic matter，hydrocarbon-generating organism and features ofhydrocarbon generation and expulsion byways such aswhole rock X-ray diffraction，combined scanning electronmicroscope and energy spectrum，and simulated experimentof hydrocarbon generation and expulsion.The results show that minerals such as quartz，calcite and dolomite in these source rocks are mainly biogenetic or related to biogenetic origin.The total organic carbon content has a positive correlation with the quartz content but a negative correlation with clay minerals content.We believe that organic matter in these source rocks have threemain occurrences:1）organicmatter associated with siliceousmatter.It is the major occurrence in the qualitymarine source rocks in South China;2）organicmatter associated with calcareousmatter.It is the main occurrence in some quality calcareous source rocks in the Permian;3）organic matter associated with clay，or coated by flaky clay particles and associated with siliceous and calcareous bioclastics.In this case，the occurrence of organic matter is mainly controlled by depositional setting and sedimentary facies.There are mainly three kinds of hydrocarbonˉgenerating organisms:algae，benthos and fungus.Samples from the same layer of source rocks commonly contain multiple parentmaterials.According to the simulated experiments，the hydrocarbon-generating potential of floating algae is the same as TypeⅠkerogen，while that of benthos is the same as TypeⅡkerogen.Super thin siliceous or calcareous layers rich in organic matters are easy to expel early-generated heavy oil，and thus a giantheavy oil poolmay be formed.In contrast，organicmatter coated by flaky clay particles are hard to expel early-generated heavy oil，and thus a light oil poolmay be formed.