Abstract: It is assumed that the infiltration process is divided into two stages of pre-infiltration and post-infiltration. The ratio of soil saturated zone to unsaturated zone is a constant 2β in the pre-infiltration stage, and the thickness of unsaturated zone increases with infiltration. The thickness of unsaturated zone in the post-infiltration stage no longer changes with time, which is a fixed value,and only the thickness of saturated zone changes with time. Based on this, Green-Ampt model is improved. The traditional Green-Ampt model and improved model were used to fit six groups of infiltration test data. The correlation coefficient of traditional model fitting was 0.982（the average of six groups of data）. Compared with the traditional model, the fitting accuracy of the improved model was obvious. The correlation coefficient was increased by 0.016, reaching 0.998 （corresponding to β=15）. The data of two groups were especially effective, which were increased by 0.07 and 0.04 respectively, both reaching over 0.99. The improved model has the same strong physical meaning as the traditional model. However, compared with the traditional model, the stable infiltration rate obtained by the improved model is closer to the test value and the improved model has wider applicability.

Key words: Green-Ampt infiltration model, accumulated infiltration capacity, unsaturated zone, infiltration front, infiltration time