Abstract: Highly compacted bentonite, as the preferred buffer/backfill material, 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 researchs of the chemical mechanism were summarized in this paper on the basis of reviewing the effect of the solution on the buffer performance of compacted bentonite. 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. Chemical cementation associated with saline precipitate filling and the cementation of aluminosilicate gelation during wet-dry cycles. The dissolution rate of minerals in bentonite is influenced by both intrinsic factors like surface area and stress, and extrinsic factors including pore solution. Further clarification of chemical reaction parameters, cementation effect, and multi-field coupling reaction model within the bentonite reaction system remains the focus of further research on the chemical evolution of bentonite in the future.