The pore types of the second member sandstones of the Xujiahe Formation in western Sichuan are dominated by secondary pores, and the primary pores in the study area are almost completely destroyed by diagenesis. The most important diagenesis affecting the reservoir includes compaction, dissolution, cementation and fracturing action. According to the comprehensive research of various data from core, thin section, casting thin section, cathodoluminescene, carbon and oxygen isotope, trace elements, fluid inclusions etc, this paper expatiates on the formation mechanism of some major diagenesis and their corresponding products, and analyzes the influences caused by the diagenesis on the reservoir. The paper points out that compaction and cementation are the main factors that destroy the primary pores of the reservoir, and that silica cementation and carbonate cementation are the main types of cementation, and the types of cements also vary in different diagenetic stage. The main reservoir space of the dissolution typed reservoir is secondary dissolution pore which is dominated by the dissolution of feldspar grains; the fractures generated by the fracturing action can improve the permeable capacity of the reservoir.
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