Tight sandstone gas reservoirs have complex reservoir structures, low permeability, and strong heterogeneity, which bring great difficulties to drainage radius and productivity analysis. Accurate calculation of drainage radius and productivity provides reliable basis for formulating efficient development plans. Therefore, it is necessary to establish adapted drainage radius and productivity calculation methods for the complex flow characteristics. This paper comprehensively considers the two-phase threshold pressure gradient and reservoirs stress sensitivity, establishes a model applicable to tight sandstone gas reservoirs horizontal well drainage radius and productivity calculation, uses MATLAB software to calculate horizontal well drainage radius and productivity using the iterative method. The effect laws of threshold pressure gradient, stress sensitivity, and water saturation on drainage radius and productivity were assessed, and the computational model's correctness and applicability were confirmed via field instances. The study's conclusions indicate that as the flu-id's flow resistance increases in proportion to the threshold pressure gradient and stress sensitivity coefficient, the drainage radius decrease. This non-linear decline trend will be further weakened by the rise in water saturation, which will further decrease the discharge radius and the formation's effective permeability of gas phase flow. The drain-age radius decrease amplitude becomes more substantial, particularly when water saturation rises from 50 to 60%. As the threshold pressure gradient and stress sensitivity coefficient increase, fluid flow is hindered and productivity drops off dramatically. The permeability attenuation of stress sensitivity runs through the entire production cycle, making the suppression of productivity by force sensitivity effect greater than that of starting pressure gradient. When water saturation increases, the ‘water lock’ effect formed by the water phase increases gas flow resistance, leading to productivity reduction. Particularly when water saturation raises from 40 to 50%, the decrease of productivity is especially notable, reflecting the sudden change characteristic of gas-water two-phase seepage mechanisms. This research accomplishment simplifies the analysis of drainage radius and the evaluation of productivity in tight sandstone gas reservoirs, takes into account the intricate flow mechanisms, and further minimizes the discrepancies between the calculation results of drainage radius and productivity in tight sandstone gas reservoirs and field actual data. It also has important guiding value for improving the recovery rate of tight sandstone gas reservoirs.