Abstract: Based on depositional environment analysis, study on diagenesis has been conducted systematically for the lower member of Xingouzui Formation of Paleogene in Mawangmiao area of Qianjiang Sag in Jianghan basin. The study results indicate that the lower member of Xingouzui Fm in Mawangmiao area was in arid and evaporated-oxidative model I sedimentary environment and half arid-humid climate, weak oxidative-weak reductive model II sedimentary environment. Accordingly, two types of reservoirs have been developed, two types of diagenesis have occurred, with quite different influence on reservoir quality due to the influence of formation water. Cementation is dominated in Model I diagenesis, with great damage to reservoir pores, and the better quality reservoirs were developed in fault zones. Model II diagenesis is dominated by chemical denudation, with positive effect on reservoir quality, and the reservoir properties are relatively good, being favorable for HC accumulation widely. This understanding provides a solid foundation for study of the diagenesis in this area, and also contribute to further exploration and development of this oil bearing area.