Abstract: The water-induced disintegration of highly clayey altered diabase is a key factors contributing to wall rock failure in diversion tunnels of the Yingliangbao Hydropower Station. To deepen the understanding of the disintegration characteristics of such rock, this study proposed a quantitative analysis method for the disintegration process. Disintegration curves were first obtained through a newly developed static disintegration test. The Logistic function was then introduced to fit the disintegration curves, based on which a quantitative scheme for staging the disintegration process was established. The average disintegration rate at each stage was accurately calculated. On this basis, the factors influencing disintegration rates were analyzed, and the disintegration mechanisms at different stages were further explored. The results show that the Logistic function can effectively fit the disintegration curves, and the defined disintegration stages closely correspond to variations in the slope of the fitted curves. The disintegration rate, as a process-based index, can serve as a quantitative indicator for evaluating and grading disintegration behavior. The proposed method provides a useful reference for studying the disintegration characteristics of similar rock types.