Upper Permian Changxing subtle reef-shoal facies gas reservoirs are developed in Yuanba Gas Field, Sichuan Basin. High-yield wells are concentrated in the northwestern part of Yuanba area where pure gas is preponderant but water areas are present in many gas traps in the eastern and the southern parts of Yuanba where middle-to low-yield gas wells are common. Different lithologic gas reservoirs are characterized by different gas-water interfaces and heights. Based on geological, logging and geophysical analysis, it is shown that the features of high-quality reservoirs, the enrichment regularity of gas accumulation and the well-matched fractures with structures are the main factors controlling the complicated gas-water relation. It is pointed out that the reef belt in the northwestern Yuanba probably is the most favorable area for exploration. This analysis result well coincides with the past predication of gas-enriching areas and gas potential zones.