Abstract: Because the mercury injection process is similar to that of hydrocarbon charging and accumulation, it is considered that the throat radius corresponding to the capillary pressure of mercury injection saturation which equals to hydrocarbon saturation of sealed?coring samples should be the effective pore throat radius threshold on the capillary pressure curves of sealed?coring samples, and the minimum effective pore throat diameter threshold in representative sealed?coring samples is the lower limit of effective pore throat of the reservoir. The paper proposes a new method to calculate the lower limit of the effective pore throat threhold of tight sandstone reservoirs accurately and rapidly. It also discusses and analyzes the advantages and limitations of the current methods. Taking He?8 reservoir of Sulige gas field as an example and based on the method of capillary pressure curve of sealed?coring samples, the obtained effective pore throat threhold of He?8 reservoir is 53.3 nm. Therefore, it is concluded that the pore systems connected by the pore throat with the radius more than 53.3 nm will be the main targets for exploration and development