Different amounts of CaCO₃ are mixed in bentonite for the purpose of simulating the characteristic changes of bentonite mixed with CaCO₃ that precipitates from groundwater around high-level radioactive waste (HLW) repositories. In the process of the project, four groups of bentonite-CaCO₃ mixtures are prepared with different contents of CaCO₃. Then a series of experiments including swell-under-load, compression and direct shear tests are carried out. The permeability coefficient is calculated through Terzaghi consolidation theory. The microstructure changes are photographed by the scanning electron microscopy (SEM). Test results indicate that: (1) The final swelling strains are related to vertical stress and CaCO₃ content. While vertical stress and CaCO₃ content increase, the final swelling strains decrease. (2) The compression index deceases slightly as the content of CaCO₃ crystals increases. (3) The permeability turns worse with increasing CaCO₃ content. (4) With the content of CaCO₃ crystals changing, the shear strength of unsaturated samples will come to its peak value. Contrary to saturated samples, the cohesive of unsaturated samples increases firstly and then increases with the increasing CaCO₃ content. (5) The photographs show that the existence of CaCO₃ fills the pores which makes the structure denser.