Accurate and timely inflow flood forecasting plays an important role in the comprehensive benefit of the Three Gorges Reservoir, and the prevention of floods and droughts, the utilization of water resources, the comprehensive management for the Yangtze River basin. Based on the optimal distribution estimation of the prediction error and the assumption of the dynamic parameters for the distribution function, a probability prediction method for the inflow flood of the Three Gorges Reservoir is proposed, and the operational test of the probability prediction of the flood is carried out. The results show that the physical rational of the presented method is clear, and it is easy to be applied and popularized in real-time operation forecast. Compared with the deterministic prediction results, the probability forecast has improved in water volume prediction and early warning effect. For example, the certainty coefficient of forecast in 1-5 d is increased by 0.1%-3.4%, and the water volume error is reduced by 0.1%-4.8%, which can provide more reliable forecast information for the real-time operation of the Three Gorges Reservoir. The proposed operational product of probability forecast of inflow flood process can provide more risk information, and provide better support for scientific and fine operation of the Three Gorges Reservoir, especially for optimal decision-making of flood resource utilization.