Abstract: Relying on the counter-tilt slope of the right bank of dam site of Zha La hydropower station in Tibet, a slope physical model is established based on geological knowledge and similarity theory. A method of staged excavation is adopted to simulate the incised action of a valley, and the evolution process of toppling deformation of a toppling rock slope is studied. The development process of deformation and fracture after excavation shows that: The toppling deformation modes of counter-tilt slope are initial unloading rebound deformation, long-term gravity bending(fracture) deformation and creep deformation in the later stage. Through the analysis of the law of displacement, deformation rate and deformation acceleration: The toppling deformation process of counter-tilt slope can be divided into 3 evolution stages(the stage of toppling initiation, the stage of steady deformation and the stage of rapid destabilization) according to the deformation acceleration a. Each stage corresponds to the deformation characteristics of attenuation creep, steady creep and accelerated creep respectively. On this basis, the deformation acceleration a is used as the criterion of slope stability, and try to use a(deformation acceleration)≥a₂(upper limit of steady-state creep) as a slope instability prediction criterion.