Abstract: The Paleogene Huagang Formation in the N gas field of Xihu Sag in the East China Sea Basin is a typical tight reservoir of low-porosity and low-permeability. Based on a large number of testing data for core property, particle size, thin section and mercury testing, the lithology, physical properties and pore structures of the reservoirs in the gas field N are carefully studied in this paper. The Huagang Formation is dominated by fine quartz sandstone with little clay. With the increase in burial depth, the intergranular pores decrease, the dissolution pores increase, and the porosity becomes worse in general, as the pore throat diameter is reduced and the connectivity deteriorated. Glutenite sometimes occurs locally, the permeability of which is more than one order higher than that of the fine sandstone, and thus becomes sweet areas for oil production. Based on the statistical results of testing data, a comprehensive evaluation standard specially applicable to the Huagang reservoir is established, which contains four important reservoir parameters, namely porosity, permeability, saturation and geological features. The classification results are distinctive and reliable. Facts prove that it is an effective tool for exploration and development of tight low-porosity and low-permeability reservoirs in the region.