This study develops a coupled model for the combined clogging and permeability coefficient of a geotextile envelope. Based on the characteristics of pore size distribution and its impact on permeability coefficient after clogging, a permeability coefficient model assuming the geotextile is composed of multiple layers of planar mesh is developed. Then, based on the range of pore size after clogging, hypotheses for large-pore clogging area and small-pore permeable area are proposed to simulate the process of decreasing the theoretical maximum pore size of the geotextile and the increasing area of large-pore clogging area. The physical and chemical clogging models are coupled and field sampling was used to confirm the availability of the model. Results indicate that the model effectively simulates the impact of clogging on the permeability coefficient. Additionally, sensitivity analysis and trend simulations show that permeability reduction coefficient (beta 1), area density (mu g0), and saturation index (SI) are the main factors affecting combined clogging and permeability, with beta 1 and mu g0 having significant early impacts, while SI has a greater impact in the later stages. When beta 1 is equal to 0.3 and SI is greater than 1.0, the geotextile envelope for subsurface drainage faces a high risk of combined clogging.