Abstract: In order to study further on the reservoir characteristics of G structure in Xihu Depression,many methods have been used,such as slice analysis,scanning electron microscopy,x-ray diffraction and so on.The study is conducted mainly on analysis of the petrological characteristics,pore types,pore structure and physical properties.The study results indicated that the rock types are dominated by feldspathic lithic sandstones,and secondly are lithic arkose.Dissolved pores between grains,dissolved pores in grains,moldic pores and primary intergranular pores are main pore types.Pore structure types are small pore,and narrow throat,being middle sorted.Huagang Fm.reservoir is middle to low porosity and middle to low permeability,Pinghu Fm.reservoir is extremely low porosity and permeability.Finally,based on the above study results,it is concluded that the sedimentation conditions,diagenesis,and abnormal overpressure are the main factors influencing the reservoir physical properties.