Under a large temperature gradient, the freezing front moves fast in a freeing soil and pore water transits into ice, resulting in local volumetric expansion. However, because the temperature gradient is generally small in a natural environment, water migrates from unfrozen areas to the freezing area, and crystalizes in some position, where pore ice accumulates and ice segregation occurs. Because the frost heave induced by ice segregation is much more significant than that induced by local volumetric expansion, it is very important to establish a model to simulate the moisture migration and ice segregation formation process. Based on the secondary heave theory, a frost heave model of freezing saturated soil is developed. The proposed model assumes that the flow rate in freezing fringe is constant for each time step. Thus, the water pressure is firstly calculated in freezing fringe, and then ice pressure is obtained based on the Clapeyron equation. The magnitude of the ice pressure is used as a criterion of ice segregation formation, with assuming that when new ice segregation occurs, old ice segregation stops growing. This model also considers the velocity of moisture migration and heave rate as basic unknown quantities, and simulates the heave under similar natural conditions where soil has overburden pressure at the top boundary and nonpressure water supply at the bottom. By comparing the numerical simulations to experimental results, the validity of the model is validated.