Abstract: The reservoir physical property of Xujiahe formation in south Sichuan is controlled by diagenesis. Research on its diagenetic facies can effectively forecast favorable reservoir area and provide reliable geological bases for exploration. The reservoir of Xujiahe formation is divided into five diagenetic facies according to the major diagenesis which control the formation and development of pore, they are the tightlycompacingt facies in shallow burial environment, the Calcium cementation facies in shallowmiddle burial environment, the Chlorite cementation facies in middle burial environment, the Silicon cementation facies in middledeep burial environment and the dissolutionKaolinite cementation facies in deep buried environment. The formation and distribution of these facies are strongly related to the original components of sediments. The reservoir property among these diagenetic facies has great difference, and the assemblage of different diagenetic facies can form dianenetic trap. Oil and gas exploration in the middle of South Sichuan(that is transitional belt of middlesouth Sichuan)should be not only in structural trap but also in diagenetic trap, because in these sections there are conditions to form diagenetic trap. 

Key words: Xujiahe formation, reservoir, diagenesis, diagenetic facies, diagenetic trap