Abstract: The highly compacted bentonite, as the preferred buffer/backfill materials, is inevitably subjected to chemical erosion in the T-H-M-C environment of the high-level radioactive waste repositories, leading to dissolution or phase transition of smectite, and diminishing the buffer performance. The latest researches on the chemical mechanism are summarized on the basis of reviewing the effects of the solution on the buffer performance of the compacted bentonite. The analysis indicates that the dissolution or phase transformation of layered smectite into a framework mineral is the key factor leading to the attenuation of the specific surface area, density, water retention, swelling and permeation resistance of bentonite. The chemical interaction mechanisms include mineral phase transformation and chemical cementation. The phase transformation of minerals is influenced by chemical composition, pH, temperature and catalytic ions of the pore solution, and can be divided into isomorphous phase transformation and recrystallization. The chemical cementation associates with saline precipitate filling and the cementation of aluminosilicate gelation during wetting-drying cycles. The dissolution rate of minerals in bentonite is influenced by both the intrinsic factors like surface area and stress, and the extrinsic factors including pore solution. Further clarification of chemical reaction parameters, cementation effects and multi-field coupling reaction model within the bentonite reaction system remains the focus of further researches on the chemical evolution of bentonite in the future.