Abstract  Based on the studies of reservoir diagenesis types and their characteristics of the Members 4 and 2 of Upper
 Triassic Xujiahe Formation in Xinchang Gasfield, it is concluded that the reservoir diagenesis mainly includes the pressolution, the authigenic mineral cementation and the dissolution. The diagenetic-reservoir facies is divided into 5 types, namely as, the intense dissolution diagenetic-reservoir facies, the chlorite lape intergranular pore diagenetic-reservoir facies, the pressolution diagenetic-reservoir facies, the carbonate cementation diagenetic-reservoir facies and the quartz secondary overgrowth diagenetic- reservoir facies. The formation conditione of the relic primary intergranular pores and secondary dissolution pores in the reservoirs are different due to tneir different diagenetic evolutionary sequences. The preservation of pores in reservoir is mainly controlled by the burial, compaction, filling of authegenic minerals and the multi-stages dissolution, as well as the chlorite laping developed in the pores. The effective diagenetic-reservoir facies in the 5 types are respectively the intense dissolution diagenetic-reservoir facies and chlorite lape intergranular pore diagenetic-reservoir facies. They play an important role in the formation of the reservoir of Members 4 and Member 2 of Xujiahe Formation , while the other diagenetic facies are ineffective for the high quality reservoir formation.