Abstract: The crude oil in Xihu Trough have the characteristics of low density、low content of paraffin、high content of saturated hydrocarbon、high value of Pr/Ph、heavier carbon isotope、mature crude oil. It reveals that the crude oil mainly come from the middle-upper Eocene Series Pinghu formation. The genetic type of natural gas can be divided into biogenic gas.thermogenetic gas、mixed gas from deeper source. The natural gas was dominated by thermogenetic gas. Dominant constituent (C₁~C₅)of natural gas in the reservoirs come from the lower Eocene Series. Minor constituent (C₆⁺) of natural gas in the reservoirs only reflecter the character of associated gas.