Abstract: Comprehensive study of 15 exploratory wells shows that the Lower Xiaganchaigou Formation have experienced a series of diagenetic evolutions and is in late diagenesis stage (A2) now. The main diageneses include compaction, pressure solution, cementation and dissolution, in which pressure solution, cementation and dissolution are the key diageneses that have large influences on reservoirs. As a whole, compaction and cementation have lowered the porosity and permeability of the reservoirs, while dissolution of cements, such as carbonate, anhydrite and gypsum, are the main factor that has improved the po-roperm characteristics of the reservoirs in Lower Xiaganchaigou Fm.