Abstract: Unsaturated seepage is an important issue in the field of geotechnical engineering. It is of important engineering and theoretical significance to carry out the contrast work between the numerical solution and the field test. A test pit immersion test was carried out on a collapsible sand site in Angola to measure the infiltration and dissipation process of water in the foundation soil. The main physical parameters of the sand were obtained by indoor test. The soil-water characteristic curve was estimated by the improved Kovács particle size method, and the curve of coefficient of permeability was estimated by the Van Genuchen model. The same water infiltration and dissipation process was simulated numerically. The similarities and differences between the measured and numerical results were compared. The results show that the sand under the free water surface is far below saturation under the condition of soaking water. Although the numerical results can reflect the macro rule of water infiltration and the dissipation process of water after water stops well, it is necessary to establish the empirical method of "saturated volumetric water content", if the range of water infiltration need accurately predicting. The "saturated volumetric water content" of the sand site is appropriate for the volumetric water content corresponding to 65% saturation.