Abstract: The extreme rainstorm after long-term and high-intensity drought will lead to the drought-flood abrupt alternation (DFAA). In order to explore the disaster mechanism of the upstream clay impervious earth rock dams under DFAA, based on the soil sample tests, the key factors affecting the expansion of shrinkage cracks are studied, and the initiation, expansion and evolution process of shrinkage cracks at different stages are analyzed. Through the centrifugal model tests, the evolution behaviors from clay impervious body defects to engineering failures under DFAA are clarified. The results show that although the high initial water content of soil can limit the occurrence of dry shrinkage cracks, it will also cause high hydraulic gradient in the soil after the occurrence of cracks, thus accelerating the development of cracks. During the first stage of DFAA, the drought process significantly reduces the permeability of soil matrix, but the shrinkage cracks caused by drought reduce the effective seepage diameter of clay impervious core and weaken its impervious performance. The extreme rainfall at the second stage causes the rapid growth of the reservoir water level, which leads to the hydraulic fracturing of the clay impervious core with cracks. The cracks penetrate the impervious core, making it completely lose its anti-seepage performance. The test results clarify the disaster-causing path of DFAA: from the change of the material performance to the danger of crack incubation to the rainfall triggered disasters.