Abstract: To investigate deterioration effect on thermal conductivity of bentonite as a buffer material in hype-temperature conditions, the bentonite powder is pretreated at different thermal aging temperatures (T=25, 100, 150, 200℃). The thermal conductivity of compacted bentonite samples after pretreatment is measured by thermal probe method, and the effect of temperature T on thermal conductivity \lambda is discussed. Based on the tests of laser particle size analysis, X-ray diffraction and thermogravimetric analysis, the microscopic mechanism of the effect of temperature T on the \lambda of bentonite samples is revealed. The results show that the λ of bentonite decreases gradually with the increase of temperature T, and the maximum decrease is 6.99%. The \lambda -T curve of the samples shows a piecewise decreasing trend with T=100℃ as the boundary point, and the deterioration effect of \lambda is more significant under high temperatures (100~200℃).The essential reason for the aforementioned changes is that when T≤100℃ (25~100℃), the temperature effect is predominantly manifested through the desorption of the free and weakly bound water, the thinning of the bound water film, the reduction of the particle size of bentonite, resulting in the reduction of the solid phase volume and the increase of the gas phase volume in the samples, which leads to the λ decreases. When T > 100℃ (100~200℃), the above temperature effect is further intensified and further reduces the particle size of the soil. On the other hand, the high temperature causes the part of montmorillonite to transform into mica sodium with high density and water absorption and low λ, resulting in a more obvious reduction of λ in the sample.