Abstract: The thermal conductivity of soils is an important thermal physical parameter for geotechnical engineering such as underground space and geothermal development. Field soils are generally under unsaturated state, and studying on the thermal conductivities of unsaturated soils has important engineering value. The thermal conductivities of quartz sand, quartz powder and kaolin clay under different degrees of compaction and different water contents are measured by using the transient state method, and the relationships between thermal conductivities of the three unsaturated soils with water content and dry density are studied. The results show that under the same degree of compaction, the thermal conductivities of quartz sand, quartz powder and kaolin clay all increase rapidly with the increase of water content before critical water contents, and then tend to be stable. The critical water content of kaolin clay is the highest, followed by quartz powder and then quartz sand. Under the same degree of compaction and the same water content, the thermal conductivity of quartz sand is the largest, followed by quartz powder and then kaolin clay. Under the same water content, the thermal conductivities of the three soils all increase linearly with the increase of dry density.