Abstract: The reservoirs of Huagang Formation in Y structure generally belong to the scope of ultra-low porosity, medium to ultralow permeability. The presence of three secondary pore zones, however, improves the reservoir properties. Based on the study of analytic data including physical property test, microscopic observation, cathode luminescence and scanning electron microscopy (SEM), it can be concluded that the dissolution pores are well developed in the reservoir of Huagang formation. Sedimentary environment is the most important factor affecting the physical properties of reservoirs in the study area. Particle size influences the physical property to some extent, and the sediments rich in debris and feldspar are advantageous to the development of dissolution pores. Another signifcant factor affecting reservoir physical property is diagenesis. The compaction and pressure solution are the main factors that deteriorate the physical properties of reservoirs. However, the dissolution makes the deep reservoir better in physical properties in local areas. The third important factor for forming the secondary pore in the study area is fault thermal event.