Frost heave is the primary cause of frost damage in cold regions. For frost-susceptible soils, water migration induced by a temperature gradient is a key factor in determining the frost heave of the soils with a water supply during the freezing process. This study looked at the effect of temperature gradients on frost heave through a series of one-directional freezing experiments for a saturated silty clay with a water supply under a variety of temperature gradients. The results indicate that the deformation and water intake of the saturated silty clay with water supply increase with the temperature gradient. The water intake of the soil begins when the freezing front drops to a critical advance rate, which is linearly related to the temperature gradient. However, even if the freezing front is stationary (advance rate of zero), a small temperature gradient is still needed to induce water intake by the soil and to cause a sizeable frost heave. The temperature gradient and the freezing rate can be regarded as two macroindexes that indicate the frost heave of soils with a water supply during the freezing process.