Abstract：Marine carbonate rocks of the Bi Qu Formation are one of the most important hydrocarbon source rocks in the North Qiangtang basin. This paper reveals the geochemical characteristics of the source rocks on the basis of the abundance， types and maturity of organic matter， and especially biomarker analysis. The results show the following: hydrocarbon source rocks occurred in the reducing environment， the organic source material is mainly lower aquatic plants mixed with some higher plants， and the organic matter of the hydrocarbon source rocks has a high degree of thermal evolution and is at a high maturity stage.