Abstract: To investigate the multi-stage behaviors of karst conduit induced water and mud inrush disasters, including the development, evolution and formation, and to reveal the evolution mechanism of karst conduit induced disasters,a large-scale model experiment system for water and mud inrush disasters was developed and the model test was conducted based on a high-speed railway karst tunnel project. The study analyzed the stability evolution law of surrounding rock and the instability characteristics during water and mud inrush disasters in karst tunnels. The results show that: (1) The development process of karst conduit induced disasters in the model test is divided into four stages: stability, seepage, inrush and attenuation. (2) The evolution of the disaster is essentially caused by excavation unloading and groundwater seepage, which lead to stress-seepage coupling. This causes fissures to form in the rock mass ahead of the tunnel face, which eventually connect to form seepage channels, leading to instability. (3) The release rate of surrounding rock pressure is used to characterize the excavation unloading effect and the rock mass seepage failure effect during the evolution of the water and mud inrush disaster. When the tunnel face is far from the karst disaster-causing structure, the surrounding rock pressure release rate is mainly controlled by excavation unloading; when it is close, the rate is mainly controlled by the water and mud inrush disaster. (4) The time-history curves of the seepage pressure, surrounding rock pressure, and surrounding rock displacement exhibit significant precursor characteristics of the disaster, which can serve as predictive indicators and identification criteria for the disaster occurrence. The inflection points of seepage pressure and surrounding rock pressure are proposed as the critical points for the instability of the anti-inrushing rock mass, and reasonable thickness values of the anti-inrushing rock mass are provided based on practical engineering considerations.