Abstract: A geometric model of frozen soil thermal conductivity is established based on a simplified definition of frozen soil as a mixture of soil column, liquid water and ice column according to the three-phase composition and the definition of thermal conductivity of saturated frozen soil. The volume calculation and evolution law of water and ice column variation with temperature is established considering the fact that the contents of the three phases in the frozen soil change with the temperature. Based on the superposition principle of the thermal effect of the parallel system, the calculation model of frozen soil thermal conductivity is established. In view of the coupling characteristics of parallel connection and series connection in the heat transfer process, a calculation model of thermal conductivity considering the effect of solid-liquid interface is established. The comparisons among the calculation results, the experimental results with transient probe method and the results by Johansen's method indicate that those methods can effectively simulate the thermal conductivity of frozen soil under different negative temperature conditions with clear concepts and simple procedures.