During the service of the high-level radioactive waste repository, low-carbon steel serves as a candidate metal material for the disposal tank, but iron corrosion products infiltrate into the buffer barrier, resulting in mineral phase transformation and performance variation, which threatens the long-term safety and stability of the multiple barrier system. This paper reviews the chemical and low-medium temperature field in the deep reduction environment of the repositories. It is believed that the above factors can cause the release of Fe²⁺ in the disposal tank. Fe²⁺ causes montmorillonite mineral phase transformation: Fe²⁺ replaces Al³⁺ and Mg²⁺ in the octahedral lattice of montmorillonite, reduces Fe³⁺ or directly occupies the vacancy to generate secondary minerals; Fe²⁺ exchanges Na⁺, K⁺ and Ca²⁺, converted to iron-based montmorillonite. Mineral phase transition can induce buffer barrier performance variation or even degradation. Based on the concept of "resisting mineral transformation", the research direction of the mineral phase transformation of the buffer material in the next stage is proposed, which provides a scientific basis for the selection of carbon steel in underground laboratories, the design of the verification test of the buffer barrier and the safety evaluation of the barrier system.