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根据冻结条件下土壤水分运动和热量迁移的基本方程，推导出了冻土水热耦合方程，并构造了采用变化的空间步长和自动调节时间步长的全隐式有限差分计算格式，使模型求解中的迭代计算过程大为简化，计算速度有很大提高。用本模型对张掖壤土的室内冻结过程进行了模拟，土壤水分、温度的计算值和试验值吻合较好。计算结果表明，该方法不仅能模拟冻结过程中土壤水分、温度的变化，且在计算中土壤含水量较低时不需要在冻结区引入冰的阻抗系数的概念，较好地改进了已有的数值模拟，为模拟各种不同条件下的土壤冻结过程创造了条件。
According to the basic equations of soil moisture movement and heat transfer under freezing conditions, the equations of hydrothermal coupling of the frozen soil are deduced. The finite implicit finite difference method with varying spatial step size and automatic time step adjustment is constructed, The iterative calculation process in the solution is greatly simplified and the calculation speed is greatly improved. The model was used to simulate the indoor freezing process of soil in Zhangye Prefecture. The calculated values of soil moisture and temperature are in good agreement with the experimental data. The results show that this method can not only simulate the change of soil moisture and temperature during the freezing process but also does not require the introduction of the impedance coefficient of ice in the freezing zone when the soil moisture content is relatively low in the calculation. Numerical simulation, to simulate a variety of conditions under the conditions of soil freezing process.