Abstract：Buffer material is one of the important engineered barriers in the high-level radioactive waste(HLW) repository. Its thermal property is one of the key properties for the design of HLW repository. ISOMET apparatus is used to measure the thermal properties of compacted mixture samples GMZM composed of Gaomiaozi Na-bentonite GMZ01，silica sand and graphite under different dry densities and different water contents. The experimental results show that thermal conductivity，thermal capacity and thermal diffusivity of GMZM increase as the dry density and water content increase. Compared with the thermal properties of GMZ01，additive of silica sand and graphite significantly increase the thermal conductivity and thermal diffusivity of compacted buffer material as the density increases. But there is no significant influence on specific thermal capacity. When the dry density is greater than 1.8 g/cm3，the thermal conductivity and thermal diffusivity of GMZM increase 20% than those of GMZ01. Thermal property of buffer material is related to water content，dry density，mineral composition and microstructure etc.. Thermal conductivity increases with the water content and dry density increase. But there is no uniform linear relationship between thermal conductivity and water content，dry density respectively. When the saturation is more than 20%，linear relationships between saturation and the thermal conductivity，thermal capacity，thermal diffusivity of compacted GMZ01 are observed respectively.
