Abstract: Based on the study of casting thin sections, scanning electron microscope analysis, X-ray diffraction, physical property analysis, and mercury intrusion porosimetry, the authors studied the diagenesis and diagenetic facies of the reservoir of 2nd member of Lower Jurassic Sangonghe Formation in Fubei area. The reservoir has experienced compaction, pressure solution, cementation and corrosion, and is now in the stage B of middle diagenetic stage. The decrease of porosity is mainly caused by compaction and cementation. Secondary pores resulting from corrosion can improve the physical property of the reservoir to some extent. According to such factors as diagenesis, diagenetic minerals and their effects on the reservoir, three types of diagenetic facies were recognized, namely facies with medium compaction, weak cementation and corrosion, facies with medium compaction, medium cementation and corrosion, facies with medium compaction, strong cementation and medium corrosion, among which the first two are the favorable diagenetic facies.