The expression of k-n is crucial in the analysis and calculation of fluid-solid coupling problems in geotechnical engineering. The relationship of k-n obtained from conventional laboratory seepage test deviates from reality as the fluid-solid coupling effect is not considered. To get a more accurate relationship between porosity and permeability coefficient, triaxial fluid-solid coupling test under varying consolidation pressure was conducted on a self-developed SRS-1 seepage and creep coupling test apparatus. The variation of porosity against time was obtained, and the fitted expressions of k-n with and without fluid-solid coupling effect are acquired. The expressions together with Kozeny-Caman's empirical formula were analyzed and then were used in the numerical simulation of one-dimensional saturated foundation consolidation in consideration of fluid-solid coupling. Then the calculation results were compared with the result of classical seepage mechanics method. Results show that 1) fluid-solid coupling effect should be taken into consideration as porosity changes dynamically in the process of seepage; 2) fluid-solid coupling problem should not be solved with classical seepage mechanics method, otherwise the error is too big; 3) since Kozeny-Caman's empirical formula, which is widely used in numerical simulation of fluid-solid coupling problem, could not accurately reflect the relationship between permeability coefficient and porosity of clay, we do not recommend it for numerical modeling; 4) the expression of k-n in consideration of fluid-solid coupling effect is recommended to improve the accuracy of numerical simulation results.