The studies of the carbon isotopic compositions of the organic carbon and organic molecules not only have special functions on the researches of the stratigraphic correlation and the oil oil and oil source rock correlations, but also widely applied in the investigations of the paleoclimate and paleoenvironment. It is necessary to study the carbon isotopic compositions and distributions of the organic carbons which are significant for the investigations of the global climate changes and global carbon cycle. It is also important to study the carbon isotopic compositions and distributions of the organic molecules in fossils and deposits which are significant for the researches of the biotic evolution and the reconstruction of paleoecology and paleoenvironment, and for the tracing of organic precursors of the organic materials in oils and source rocks.