Abstract: Analysis of laboratory data indicates that the Jurassic reservoir of Ke-Bai area in northwestern margin of Junggar basin experienced compaction, cementation, dissolution and other diagenetic processes. Compaction and dissolution are main diagenetic processes that control the reservoir quality. The compaction is the major reason for reducing storage space. It is here dominated by the mechanical compaction with little significance of compaction-dissolution. The cementation is mainly of carbonate character,with little pyrite-cementation and less analcidite- and kiesel-cementation. The dissolution comprises cabonate cement dissolution,lithic grains dissolution and detrital feldspar dissolution. The reservoir pores evolved from primary to secondary pores. The pore space was affected by the dissolution of calcite and feldspar, as well as the precipitation and cementation of carbonates. The cementation by early calcite is favorable for the development of secondary pores in the later stage. The difference between the reservoir characteristics for different walls of the fault belt is obvious. On the hanging wall of the fault belt, the burial depth of strata is shallower, less than 1800 m, and the storage space is characterized by primary pores; However, on the foot wall of the fault belt, the burial depth of strata is deeper. Because of strong compaction, the proportion of the primary pores become obviously less, and the secondary pores are the major storage space. The characteristics of the secondary pore distribution are controlled by the distribution of acid fluid and fault.