Abstract: The ability to generate oil of northern main low-lying of Herisitai sag is analyzed by using hydrocarbon source rock 'organic matter abundance,organic matter type,degree of organic metamorphism,expulsion efficiency of hydrocarbon,etc.On the basis of area-pore ratio,expulsion pressure,expulsion efficiency of mercury,and core's data of porosity and permeability by practical measurement,the reservoir is evaluated and the condition of the trap is analyzed.Accord-ing to the research,it is indicated that the low-lying has the ability to generate oil to a certain degree and to form val-id trap,but the reservoir's capability of storage is poor.