The effective stress coefficient determines the effective stress, which dominating the permeability of rocks. However, the documented value of for rocks shows a high scatter (0.3-5.5), based on the laboratory measurement. The well know Clay Shell Model (CSM) successfully explain why the of the clayey sandstone can well above 1 theoretically. However, CSM cannot account for the stress dependency of observed experimentally. In this study, a modification of CSM was proposed. This proposed Discretized Clay Shell Model (DCSM) discretizing multi-layers clay domain to account for the stress dependent elastic modulus of clay. Response surface method was used to determine the effective stress coefficient under different combination of confining stress and pore pressure. The parametric study and the prediction of permeability-depth relation using synthetic case illustrate the superior features of the proposed DCSM to the traditional CSM, especially when the clay content is high. Critical findings includes: (1) The predicted effective stress coefficient form a concaving upward surface in the pore pressure-confining stress space using DCSM even when the material properties of clay and grain remain unchanged. (2) The influence of pore pressure on (positive correlation) will be stronger than the influence of confining stress especially under low pore pressure. (3) The predicted is not necessary positively or negatively correlated to confining stress under constant pore pressure. (4) The predicted for soft, high stress dependent deformability of clay coating on the pores of sandstones could be far higher than 1.