Abstract: Moisture transfer in soil plays an important role on the subgrade soil frost heave, and the water content and temperature gradient are the main factors affecting soil moisture migration. Unilateral freezing test was carried out with the indoor moisture migration test apparatus, which can adjust the initial moisture content and the top temperature to explore the effects of moisture and temperature gradient on the soil moisture migration and soil freezing process. The results showed that, in the upper area of the frozen sample soil, irregular reticular cracks occurred. Inside the densest section of the cracks, a large number of ice crystals existed, making the water content peaks in the soil sample. The magnitude of the water content peak was mainly affected by the initial moisture content, while the location was mainly determined by the temperature gradient. The increased water content of the upper frozen zone came from the external water supplement and moisture migration from the unfrozen zone. Correspondingly, the moisture content of the lower unfrozen zone decreased, and the decrease was mainly affected by the initial moisture content. During the whole freezing process, the external water remained migrating into the soil, and the speed of water migration increased initially and then decreased. The increase in temperature gradient would increase both water intake and flux rate. The higher the initial moisture content, the smaller the water intake would be obtained. The frost heaving rate and the freezing rate were mainly affected by the temperature gradient. The overall trend initially increased to a peak, then gradually decreased and finally stabilized. Thus, a slight increase in initial water content in soil can reduce the amount of water migration in the freezing process, and the frost heave of soil can be decreased and delayed obviously by increasing the thickness of pavement structure so as to reduce the frost temperature gradient inside the subgrade soil.