Abstract: By comparing and analyzing two methods (Kunze’s method and Fredlund’s method) based on statistical models to predicting the hydraulic conductivity of unsaturated soils, we found that they are exactly the same in essence just with different limits of integration and integration variable forms. Moreover, by analyzing the selection of parameters in their simplified calculation we obtain that it is more reasonable to determine the value of m within 15-50. Theoretically the prediction result will be larger if ln(1000000) (residual water content is assumed to be 0) is taken as the integration upper limit and logarithm of air-entry value as the integration lower limit in Fredlund method.

Key words: unsaturated soil, hydraulic conductivity, statistical model, Kunze’s method, Fredlund’s method, residual water content