Tight gas reservoirs in the S area exhibit poor physical properties and complex gas-water relationships. During production development, threshold pressure gradient and stress sensitivity significantly impair gas well productivity and the utilization of residual gas reserves. Conventional laboratory methods for threshold pressure gradient measurement face limitations in testing accuracy and unclear theoretical principles. Additionally, laboratory constraints prevent the simulation of actual reservoir pressures during stress sensitivity experiments, leading to overestimated stress sensitivity evaluations. To address these issues, this study improves the experimental apparatus for threshold pressure gradient measurement. The bubble method is employed to test cores with varying permeability and water saturation, achieving a precision of 0.01 kPa. Stress sensitivity is evaluated by fitting experimental curves obtained under low-pressure conditions and extrapolating them to actual reservoir effective stress. The results show that: Threshold pressure gradient increases with deteriorating reservoir quality and higher water saturation; under identical water saturation, poorer reservoir quality correlates with stronger stress sensitivity and irreversible permeability damage; When reservoir pressure decreases from the original formation pressure (30 MPa) to 15 MPa, the reservoir is classified as weakly stress-sensitive; The microscopic pore-throat structure and petrological characteristics of the reservoir jointly govern gas-phase flow resistance, high capillary pressure induced by micro-scale pores and throats, the Jamin effect, and water-rock interactions are identified as the primary mechanisms responsible for the threshold pressure gradient and stress sensitivity in water-bearing tight sandstone reservoirs. Field strategies—including maintaining formation pressure, minimizing well shut-ins, and optimizing dewatering-gas production are critical for sustaining productivity and enhancing distant-zone recovery. These results systematically characterize Threshold pressure gradient and stress sensitivity in S-area reservoirs, providing foundational insights for modeling gas-water flow behavior and constructing productivity prediction models in tight sandstone reservoirs.