The data of thin section, cast slice, SEM, X-ray diffraction, mercury injection combining with geological information and physical properties analysis are applied to analyze the characteristics of N₁—N₂¹ and the difference between the upper wall and lower wall of fault Ⅱ in Shaxi zone. The result shows that the reservoir in the study area is clastic reservoir which experienced destructive diagenesis of compaction and cementation and constructive diagenesis of dissolution and tectonism. The diagenetic stage is in the period from early diagenesis subage B to late diagenesis subage A1. The pore structure types are intergranular pore, intragranular pore, and fracture etc. The reservoir of N₁—N₂¹ is middle pore and low permeability reservoir with poor property. Distributary channel sand bodies are the foremost reservoirs in the study area. The compositional maturity of the lower wall is much better than that of the upper wall of fault Ⅱ, however the cement content is on the contrary. The sandstone in upper wall is mainly the feldspathic litharenite, and in the lower wall it is mainly the arkose. The pore in upper wall is mainly intergranular pore, however, fracture developed well in lower wall. The reservoir is medium porosity and medium permeability in upper wall but low porosity and low permeability in lower wall.