Abstract: In this paper, a mathematical model is designed to estimate the water containment risk for high rock-fill dams during interim seasonal flooding based on the condition that the water must not flow over the top of the dam, and other stochastic factors such as the level of the floodwater in front of the dam and the high water level during flooding. The characteristics of rock-fill dam construction systems, the number of days each month when the dam is under maintenance, and the stochasticity of the average speed of the increase in water level per day are considered for designing a model to calculate the simulated height for flood prevention during interim flooding. Based on the Monte Carlo method, the created risk model is solved by linking stochastic elements from hydrology, hydropower, and construction. Further, the influence of the controllable construction indicator, which is the minimum average daily rising speed, on the risk rate is researched. The feasibility and effectiveness of the risk model and the calculation method are demonstrated through the analysis of Changheba hydropower station in the Dadu River basin in Sichuan, China.