In order to study the distribution of water in silt soil subgrade, this paper establish finite element model based on unsaturated seepage theory to research the groundwater level, rainfall, evaporation factors influencing on the moisture content of subgrade and side slope materials. The results show that: the moisture content of suhbgrade exponential growth with the water table. Continuous evaporation or rainfall influence the subgrade slope with the depth of 0.2–0.6m; finite element model based on unsaturated seepage theory can predict the water content in subgrade accurately and meet the project construction need.