Abstract: The Kozeny-Carman equation has definite physical meaning, and can be widely used in calculating the permeability coefficient of sand.In order to improve the accuracy of using the conventional Kozeny-Carman equation to predict the permeability coefficient for saturated clay, firstly, the theoretical model for equal spherical particle is established, quantifying the share of absorbed water film occupied total pore space, so the permeability is greatly affected.According to the relationship between Atterberg limits and content of absorbed water film, the formula for calculating the efficient void ratio is derivated by the liquid limit.Then, the conventional Kozeny-Carman equation is modified.Finally, the proportion coefficient of absorbed water quality to liquid limit in Hefei clay is calculated by thermal gravimetric tests.Substituting the relevant physical parameters of Hefei clay into the unmodified and modified Kozeny-Carman equation, by comparing the calculated permeability coefficient with the measured value of laboratory tests, the results show that the modified Kozeny-Carman equation can be more accurate for estimating the permeability coefficient of clay.