Abstract: As the preferred buffer/backfill material of deep geological disposal for high-level radioactive waste, the long-term stability of Gaomiaozi bentonite's barrier function needs further study. In this paper, the rheometer was used to measure the shear strength of Gaomiaozi bentonite with different standing ages(hereinafter referred to as the setting strength), to explore its characteristics and mechanism of changes. Basing on the dynamic balance study of the bond breakage and reconstruction of bentonite particles, a tensile index model was improved to reflect the evolution of bentonite strength over time. With the prolonging of standing time, the microstructure of bentonite gradually tends to be uniform. The bentonite particles with extremely low electrolyte content tend to be overlapped, and the setting strength will be significantly improved; while the bentonite particles with higher electrolyte content are always parallel lapped, and the setting strength basically unchanged. This paper provides practical experience for the design, construction and long-term safety evaluation of the geological repository for high-level radioactive waste, which can also be helpful for the study of thixotropic hardening of ordinary clay.