A moisture migration test for unsaturated clayey loess along the SHERFPL is done to understand the water migration of soil under a closed system in freezing condition. The experimental data shows that the temperature decreases with the slope degrading and eventually reaches a stable temperature gradient. Temperature potential has little effect on soil’s moisture migration. The formation of the gradient of soil’s water content is mainly caused by temperature gradient. With temperature decreasing to the freezing temperature of soil, the unfrozen water content decreases quickly in frozen zone. Such decrease results in the great drop of matric potential, making unfrozen water migrate toward the lower temperature zone. Based on the model test, a coupled heat-fluid transport equation is built and simulated by a two-dimensional finite element model, from which the temperature and moisture field of the specimen under closed system are obtained. It is found that the obtained results are closely agreed with the experimental data. Therefore, the model is adapted to simulate the variations of temperature and moisture of subgrade soil during freezing process in seasonal frozen ground, which can provide the basis for inhibiting frost heave.