Abstract: Fluid-rock interaction is critical for the formation of tight sandstone reservoirs, contributing to illustrate the distribution of high-quality reservoirs. In this study, a simulation experiment on the co-evolution of type Ⅲ source rock fluids and feldspar-quartz sandstone reservoirs under sealed condition was carried out with the samples from the Upper Triassic Xujiahe Formation in the western Sichuan province. A large amount of CO₂ generated leads to the development of carbonate cements in sandstone reservoirs at temperature of~140 or 170℃, indicating the main factors for sandstone reservoir densification. The retention effect of hydrocarbon fluids plays a key role for reservoir densification. In the closed diagenetic system, tight oil and gas exploration should focus on locating favorable sedimentary sand bodies that are conducive to the formation and preservation of primary pores; while in a semi-open or open system, it should be directed to reservoirs with secondary pores in the dominant migration and accumulation areas of acid fluids.