Abstract: The soil infiltrability has a close relationship with overland flow and groundwater, determining the fraction of the irrigation or rain water entering the soil, the transportation of chemicals such as fertilizers, herbicides/pesticides as well as other pollutants，and，thus, affecting the amount of runoff responsible for subsequent soil erosion. Based on the energy principle of water movement in saturated/unsaturated soils and the measured soil water distribution in horizontal soil column, modifications were made to the piston assumption of the soil water distribution in the Green-Ampt infiltration model. The soil water distribution was described by a more realistic linear distribution model. Based on the water/mass balance and the soil water dynamics, a modified mathematic model for soil infiltrability estimation was advanced. The measurement method, algorithm models and procedures were given for estimating soil infiltrability with measured data from horizontal soil column. Comparisons of the cumulative infiltration computed from the estimated infiltrability with the modified method and the total supplied water indicated that the relative error was 0.66%, which demonstrated a very high accuracy of the model and the computational method. The modified model can describe the distribution of the soil water very well which is more suitable to the analyzations in the soil water dynamics than the piston assumption in the Green-Ampt infiltration model. The accuracy can be greatly improved by applying the modified model to the horizontal soil column experiment. This can supply a very useful tool to the relative studies such as the soil water movement analysis, overland flow estimation and soil erosion analysis.