Abstract: To establish a reliability index and instability probability calculation method for rocky slopes in the hydro-fluctuation belt of the Three Gorges Reservoir, we established a mechanical model for the rocky slope in the hydro-fluctuation belt under different water pressure distribution assumptions, which was based on the method of limit balance and reliability analysis. In this study, two cases, the outflow fissure blocked and not blocked were considered respectively. The reliability calculation was carried out for Jianchuandong rocky slope in the reservoir area. It was showed that the instability probability was 26.76%, which was in a basic stability condition and in excellent agreement with the actual situation. The influence law of each sensitive factor on the failure probability of the rocky slope was analyzed in detail by using the control variable method. The results showed that the stability coefficient was decreased directly and the failure probability was increased with the increase of slip surface dip. Moreover, when the cohesive strength, internal friction angle and trailing edge crack inclination increased, the stability coefficient increased and failure probability decreased. The results can provide a new method and theoretical basis for the stability analysis of the rocky slope in the hydro-fluctuation belt of the Three Gorges Reservoir.