Abstract: The reservoir characteristics of the 4~(th) member of Shahejie formation in WXO well block of Langgu depression were studied through cores observation, rock thin section identification, physical properties analysis and the mercury injection, the results indicate the reservoir characteristics of the 4~(th) member 4 of Shahejie formation in WXO well block are mainly of fine-silt feldspar sandstone, the reservoir belongs to low porosity, ultra-low permeability reservoir, and the pore throat structure is of wide-fine throat type. The main reservoir spaces are original intergranular pores, inter-granular dissolution pores, intragranular dissolution pores and the fracture is less. The diageneses contain compaction, cementation, dissolution and metasomasis. The diagenetic experienced early diagenetic B stage and late diagenetic A and B stage. Sedimentation and diagenesis have an important influence on physical properties of reservoir. The sedimentation determines the favorable the sedimentary facies, and the subsea distributary channel and mouth bar were favorable facies belt for hydrocarbon accumulation. The compaction and cementation make the properties of reservoir poor, the dissolution leads to secondary pores, which increases the porosity and permeability of the reservoirs.