Abstract: The source rock, hydrocarbon generation, source kitchen and trap formation are discussed aimed at Xiaoheba FM of lower Silurian in the eastern Sichuan Basin, which is called natural gas reservoir geochemistry researches. First, through natural gas components, carbon isotope and organic faces analyses, dark shale and gray mudstone of longmaxi FM having high hydrocar-
bon generation potential are thought as the source tock of Xiao-heba Natural gas reservoir. Second, the peak moment of hydro-carbon generation is clear and two large-scale source kitchens are determined by buried history research andTTIcalculation. Third, structure trap formation moment is in accordance with
the peak moment of hydrocarbon production.Forth,the result of fluid inclusion analysis testifies that the critical moment is late Triassic-early Jurassic.In the end,the system of reservoir forma-tion is constructed and natural gas reservoir forming process is clear.

Key words: Sichuan basin, natural gas, organic faces, iso-tope