Abstract: The hydrocarbon geochemical anomalies in the Haijiao Uplift and the Zhejiang Fujian Upfold are the result of upwards seepage of hydrocarbon in the deep pre Cenozoic sedimentary basin.The analytical data of wetness coefficient of acid extracted hydrocarbon of sediment and its δ¹³ C₁ shows that the gas in Qiantang Sag,the Zhoushan Islands and the offshore area around Shanghai are mainly from the thermal cracking of natural gas in deep.They are similar with the gas in Xihu Sag and the Haijiao Uplift which is the over matured gas of deep part.The alkane hydrocarbon abundance index of the gas from Zhejiang Fujian Upfold is higher than that from Pinghu 5 well.