Abstract: In order to make clear the relationship between the porosity and the production capacity of the low permeability sandstone reservoir in Huagang Formation of the Xihu Depression, pore structures are studied. More than 500 cores data and 311 conventional mercury testing data are used. By the correlation analysis between the characteristic parameters of microscopic pore structure and macroscopic physical properties, choosing the maximum connected pore-throat radius and average connectivity of pore-throat radius as the favorable parameters for throat grading and using the method of data configuration, the paper determined the pore structure classification standards and established the new classification system that suitable for low permeability gas reservoir in this area. The pore structure of Huagang Formation H3 sandstone reservoir could be divided into six types including big-mid pore with coarse throat type, mid-small pore with mid throat type, mid-small pore with mid-fine throat type, small pore with fine throat type, small-fine pore with micro-fine throat type and fine pore with micro throat type. According to the classification of pore structure, the reservoir could be grouped into four types with the production capacity corresponding to high, middle, low, and ultra-low yield respectively. The first kind of reservoir corresponding to the big-mid pore with coarse throat type and the mid-small pore with mid throat type, of which porosity and permeability were higher as well as the capacity of yield, is the most favored reservoir.