The geological disasters in the permafrost regions of Tibet Plateau are closely related to the water redistribution caused by the freezing and thawing of frozen soils, which is the result of complex hydro-thermo coupled process intrinsically. The current hydro-thermo coupled models of frozen soil are mainly designed to describe the water migration process driven by the gradient of unfrozen moisture content, yet the effect of temperature gradient on the coupling process is rarely considered. Based on the classical heat transfer equation and seepage theory of unsaturated soil, a hydro-thermo coupled model driven by double gradients for unsaturated frozen soil was established, in which the combined influence of unfrozen water content gradient and temperature gradient was considered. Then, the proposed model was verified by experimental results, after which a series of numerical simulations were carried out on the hydro-thermo response of the soil under three environmental temperatures, -5, -10 and -15 ℃. The results show that the driving effect of temperature gradient on water migration in the freezing process cannot be ignored. During the freezing process, the freezing rate gradually slows down due to the latent heat released by the phase change of ice-water. The location of water accumulation is at the frozen front formed at the beginning of freezing process. Furthermore, the lower the outside temperature, the greater the internal and external temperature difference, the deeper the location where water accumulates, and the greater the amount of water migration. In addition, the moisture content presents an S-shaped distribution with the depth during the freezing process. Specifically, extreme values of moisture content at -5, -10 and -15℃ are at the depth of 0.30, 0.55 and 0.70 m, and the corresponding increment of moisture content is 3.5%, 4.6% and 5.5%, respectively.