Abstract: The research of thermal conductivity in unsaturated soils is of great significance in various fields such as geotechnical engineering,agricultural production,environmental preservation,and soil physical properties. Nevertheless,the traditional methods used to measure thermal conductivity of unsaturated soils have certain limitations. This study employed the transient plane source method to measure the thermal conductivity of unsaturated soils and calibrated both the double-sided and single-sided transient plane source methods. The single-sided method does not require the insertion of probes or sensors during the process of measurements,thus minimizing disturbances to the soil structure to the maximum extent. The study measured the thermal conductivity of sand,silt,and clay at different saturation levels to explore the relationship between thermal conductivity and saturation for these three unsaturated soil types. The results show that it is effective to measure the thermal conductivity of unsaturated soils by using the transient plane source two-sided method and single-sided method,and the thermal conductivity of the three soils increases with the increase of saturation. However,the thermal conductivity of different soil types varies significantly with the degree of saturation. When sand transitions from a dry state to a residual saturated state,its heat transfer capacity increases dramatically. However,as the soil approaches full saturation,the increase in thermal conductivity becomes less noticeable. Compared with sand,the thermal conductivity of silt and clay changes more smoothly with the increase of saturation.