Based on analysis of cast sections, X-ray diffraction, vitrinite reflectance, scanning electronic microscope and cathodoluminescence, this paper analyzed and evaluated the characteristics of petrology, reservoir physical properties, diagenesis, diagenetic stage and reservoir microstructure of the Chang 2 oil reservoir bet in Longzuigou area of Xiasiwan in Ordos basin. The results show that the Chang 2 oil reservoir set mainly developed medium and fine-grained lithic arkose. Its pore type is mainly intergranular pore and the main throat type is dominated by punctate throat. The diagenesis types are mainly compaction, cementation, replacement and dissolution. The compaction has the most destructive effect on reservoir physical properties in the process of porosity evolution, followed by cementation and replacement, while
dissolution improves the reservoir pore significantly. Combined the analysis data of the fluid inclusion and the vitrinite reflectance, it is considered that the Chang 2 oil reservoir set in Longzuigou area is now in the middle diagenetic stage A.