Abstract: Laboratory tests are conducted on the compacted Gaomiaozi (GMZ) bentonite by using the DIL 806 thermal dilatometer. The influences of different factors on the thermal expansion properties of the bentonite are systematically analyzed. The thermal expansion coefficient of the bentonite is obtained with the dry density, the heating rate, the water content and the atmosphere environment. The experimental results show that the coefficient of thermal expansion increases with the dry density of the bentonite. The coefficient of thermal expansion decreases with the increase of the initial water content. The coefficient of thermal expansion increases with the increase of the heating rate for the samples with high water content, and the coefficient of thermal expansion decreases with the increase of the heating rate for the drying bentonite. Under the same dry density and water content of the samples, the coefficient of thermal expansion is higher in the air environment than that in the Ar gas environment. The research results have certain reference for analyzing the thermal expansion properties of the bentonite and evaluating the long-term stability of buffer materials for high-level radioactive waste disposal.