The successful exploration of natural gas in Shahezi formation opened the prelude for sandy conglomerate gas in faulted formation of Xujiaweizi depression in Songliao basin.Sandy conglomerateare characteristics by high interstitial fillings, complex types and various origins.The relationship between interstitial material and sandy conglomerate is unclear, which restricts the effective reservoir prediction.According to characterization of thin section, scanning electron microscope, X diffraction, physical testing, the types of interstitial fillings and the influence on sandy conglomerate reservoir are analyzed. The results show that the interstitial material types include mud matrix, volcano ash, carbonate, siliceous,clay minerals, pyrite,etc.The main interstitial fillings are mud matrix and carbonate,followed by clay minerals, silica and volcanic ash,with pyrite seldom developed.Mudmatrix and volcano ashare sedimentary fillings,silica and clay minerals are formed in the early to middle diageneticstage, and carbonate cements are mostly developed in late diagenetic stages.The relationship between interstitial fillings types and rock porosity indicates that mudmatrix plugs the pore throat and reduces original pore greatly. Siliceous cementation and chlorite cladding in the early diagenetic stage increase reservoir strength, which is conducive to the preservation of primary porosity. The volcano ash is easy to be dissolved, which is favorable for the development of secondary pores.Large poresare devided into small pores by clay mineral and a large number of micro pores are provided,so clay mineral content and the porosity are negatively correlated.Residual poresare filled by late carbonate cements,which increase the density of sandy conglomerate.