Abstract: The compressive strength value is commonly used to characterize the mechanical properties of bentonite buffer materials in deep geological disposal repositories. The unconfined compressive strength test is used to study the variation of the mechanical property of MX-80 bentonite after alkali-thermal treatment. By X-ray diffraction (XRD) and mercury intrusion porosimetry (MIP) tests, the evolution of mineral composition and pore distribution of MX-80 bentonite samples is studied, and the microscopic mechanism of mechanical property deterioration of the samples is revealed. The deterioration model of mechanical property of samples is established. The results show that after alkali-thermal action, the unconfined compressive strength q_u of the bentonite samples decreases with the increase of the pH and the environment temperature T. Higher pH and temperature lead to a more significant decrease in the unconfined compressive strength q_u of the samples. The fundamental reason for the deterioration of mechanical properties of bentonite above is that the main clay mineral (montmorillonite) is corroded by alkali solution, and part of it is converted into the analcime with a weak expansion, which increases the internal porosity of the samples, and the temperature T plays a good promoting role. The established model can effectively predict the deterioration trend of the mechanical properties of bentonite samples after alkali-thermal action.