Abstract: The accumulation factor of a petroleum system is the ratio between the amount of the oil and gas accumulated (resource)and the hydrocarbon-generating,and it's the key parameter to evaluation for the oil and gas resources.The Pucheng area is a high-in-sag structural geological unit,in which the exploration degree is high,the geological knowledge is known well,the proven degree for the resource is high as well.It has a clear boundary to supply the oil and gas.The character of the oil and gas reservoir,the formation conditions and the hydrocarbon accumulation history are known well.This system can be thought as a independent and integrated oil and gas accumulation unit surrounded by the separated grooves with the similar characteristics of oil and gas migration.The research on this accumulation factor can be effective to the evaluation for each geological factor.In this paper the basin-modeling method is used to calculate the amount of hydrocarbon from the effective source rocks in the biggest source kitchen,then based on the preven reserves,use the oil reservoir order method and the Wong's circle method to calculate the final proven reserves,in turn to calculate reversely the accumulation factors of this system:the value is 12.9%～15.6% for oil and 0.905% for gas.The result is significant to the research on the oil and gas accumulation factors for the exploration area that has similar geology conditions.