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Aimed at the salinization problem of aeolian sand subgrades in desert areas over time, which has not been sufficiently considered in the Ejina region, China, based on multifield coupled numerical simulations with COMSOL Multiphysics and indoor one-dimensional soil column tests, the water and salt migration process in aeolian sand subgrades under a temperature gradient was analysed. The temporal and spatial variations in the temperature, moisture, and salinity in the subgrade salinization process were determined. Selecting a salinization rate of 0.3% accumulated 10 cm below the top of the subgrade as a critical criterion, a regression equation between the salinization time of the aeolian sand subgrade and the initial subgrade moisture content and salinity was established via nonlinear regression analysis. The results show that the temperature inside the subgrade is nonlinear along the depth direction, and the transmission process is accompanied by the attenuation of energy, which establishes a temperature gradient. The moisture and salt contents of the subgrade gradually decrease from bottom to top and are influenced by the pavement coverage effect and temperature gradient. There is a water-salt accumulation zone on the surface of the subgrade. The measured salt content at points in the soil column test agrees well with the simulation results, and the distribution law of water and salt obtained by the model is in good agreement with the water and salt variations in the simultaneous heat and water transfer model. The salinization time of the aeolian sand subgrade is affected by both the initial moisture and salt contents of the subgrade, and the influence of the initial salt content is more notable. The research results have a theoretical guiding significance for the control and prevention of salinization in desert areas.