Abstract: Fossil in the Middle Jurassic Yaojie Formation,Yaojie,Gansu and modern Ginkgo cuticle organic components and organic carbon isotopic composition have been analy sed in this paper.It's shown that Gink gocuticles have a high chemical resistance tow ards wea thering and there is a similar a lkanes and terpenes and steroids components between fossil and modern Ginkgo cuticles.Paleoenvironment can be recon structed by using carbon isotopic compositions and other parameters of Ginkgo cuticles.The result canbe made that paleoenvironment was warm and wet in the early,and became graduallya rid and little rain after middlep eriod,and then rainfall and temperature increa sed,vegetation developed in the late of Middle Jurassic series.