Based on a randomly mixed model, in which the constituent parts of the multi-phase medium are all cubic in shape, uniform in size and randomly dispersed, the effective thermal conductivity of the medium is obtained from the thermal properties and volume fractions of the components. Compared with the experimental data, the present model can give fine predictions of the effective thermal conductivity of soils. Factors related to the thermal conductivity and heat storage coefficient of the soil are investigated, and the results show that the effective thermal properties of the soil dependent on the type of soil, the porosity, the degree of saturation and the state of the water. In addition, the difference of the thermal characteristics between the frozen and unfrozen soils is discussed.