•A model is proposed to describe the water-heat coupling process during freezing.•Unfrozen water function for saline soil is determined and applied in modeling.•Frozen depth of the saline region is predicted based on the coupling analysis.•Finale ice formation and water dynamics are simulated and validated.•Temperature variation hysteresis in soil profile is proved and analysed. Frozen depth has a great significance for the foundation engineering in cold regions, always showing a high correlation with some attendant engineering phenomena, including water aggregation, frost heave, and salt accumulation. To study the heat-water dynamics and frozen depth characteristics during the freezing process, soils in western Jilin Province of China, a typical seasonal frozen region, were selected for investigation. A coupled heat and water model was proposed to describe the water-heat coupling process during freezing, with full consideration of the unfrozen water variation, the ice layer formation, and the interaction among different elements. Then, the dynamics of the heat-water and frozen depth were simulated based on the boundary conditions of temperature variation with reference to the meteorological data. The in- situ monitoring data from the whole winter were used to analyse the model performance. The results show that water content and temperature data match the test data, and the Root Mean Square Error (RMSE) values of the temperatures (within 2 °C) at different depths were acceptable, indicating that the water-heat dynamics can predict the maximum frozen depth well. In addition, the temperature of the soil profile varies rapidly in the first 60 days of winter, and the frozen depth continues to increase even though the temperature starts to rise after freezing for 80 days. The moisture transfers upwards with the effect of heat flow, and the formation of ice occurred mainly at a depth of 1.5 m. Heat conduction plays an important role in modelling, predominantly leading to the hysteresis in the frozen depth variation during freezing. This new method can provide a reference for water-heat movement and the prediction of the frozen depth during freezing in the saline soil regions.