Abstract: Risk of overtopping during the construction period of earth-rock dam is not only controlled by flood level, but also by the top elevation of water retaining structure. With these two factors simulated by Monte-Carlo simulation, their distributions have been determined via analysis on the uncertainties in hydrologic and hydraulic factors and the uncertainties of construction progresses, the overtopping risk for each stage and the integrated overtopping risk have been calculated using a mathematical model that was developed for calculation of different water diversion stages. The case study shows that the uncertainties of construction progresses have significant effects on overtopping risk during the construction period of earth-rock dam, the calculation methods and models are practicable.