It is prevalently known that the presursor of marine hydrocarbon source rock is derived from bacteria and algae so as to good types of organic matter and good hydrocarbon- generating potential. However in recent years, this pointview of the single organic quality is still deliberative. The organic quality of Mesozoic and upper Paleozoic hydrocarbon source rocks in Nanling-Wuwei area in Anhui reveals a dual property. The data of kerogen microscopic analysis and carbon isotope show the type of sapropel kerogen while the data of kerogen elementary ratio and Rock-Eval, which are the parameters of the hydrocarbon-generating potential of the organic matter, indicate the equivalent Type-Ⅲ. It is not always suitable that taking the original source replaces the hydrocarbon-generating potential. The degradation ratio of sapropel kerogen is not always high, which is important to evaluate the potential of marine hydrocarbon source rock.