The resource potential of the Xujiahe Formation in the Sichuan Basin is immense; however, its complex gas-water distribution patterns severely restrict the advancement of subsequent exploration deployment. Relying on experimental methods such as casting thin sections and high-pressure mercury injection, this paper systematically analyzed the basic geological characteristics, gas-water distribution patterns, and main controlling factors of the tight sandstone gas reservoirs in the third member of the Xujiahe Formation in northwestern Sichuan. The results show that the reservoirs exhibit overall low-porosity and low-permeability characteristics, with an average porosity of 3.14% and an average permeability of 0.052 mD. Three main types of source-reservoir configurations are developed in the area: self-sourcing and self-reservoiring, laterally-sourced and laterally-reservoired, and lower-sourced and upper-reservoired. Among these, the self-sourcing and self-reservoiring type exhibits the closest contact and the highest natural gas charging efficiency. The gas reservoirs present a planar cross-distribution of high- and low-production wells and a vertical trend of “gas above, rich water below”, with no unified gas-water contact across the region. The early paleo-structural slope provided favorable sites for natural gas accumulation, while late-stage reservoir densification effectively preserved the gas reservoirs. Fault hierarchy strictly controls productivity variations: fourth-order faults and high-quality reservoirs with porosity greater than 6% are favorable zones for natural gas enrichment, whereas first- and second-order faults predominantly produce formation water. Moreover, a higher fracture linear density in a single well correlates with higher natural gas productivity. It is concluded that gas-water enrichment in the third member of the Xujiahe Formation in northwestern Sichuan is jointly controlled by early fault conduits and late-stage reservoir densification. The quality of the source-reservoir configuration determines the natural gas charging intensity, and the gas-water distribution regulated by these factors exhibits strong heterogeneity characterized by “horizontal cross-distribution and vertical gas-over-water.” On this basis, a gas-water enrichment model featuring “enrichment by favorable source-reservoir relationship, fault adjustment, and fracture-controlled production” was established. This model effectively clarifies the deep-seated main controlling factors responsible for the huge disparity in productivity between high- and low-production wells and the cross-distribution of gas and water. It clearly identifies that the superimposed development zones of fault-fracture bodies, paleo-structural highs, and reservoirs with high porosity and permeability are the dominant target areas for high natural gas production. The research findings deepen the geological understanding of the complex accumulation and enrichment laws of unconventional tight gas in the Sichuan Basin. They not only point out the direction for subsequent efficient exploration and well placement in northwestern Sichuan, but also provide important theoretical references and practical guidance for the exploration and development of tight sandstone gas reservoirs with complex gas-water relationships in similar sedimentary basins.