The upstream flood water is the major risk factor of reservoir risk scheduling. According to the principles of disaster risk analysis, the risk of weather forecasting service for reservoir dispatching is analyzed. The results indicate that the veracity of precipitation forecast and stream modulus are the major risk factors of forecasting service for reservoir dispatching. An practical risk analysis model is thus built. The model was used in the forecasting service for reservoir dispatching during the attack of typhoon Sinlaku, and the economical benefit is calculated. The model has proved useful for the decision-making of water conservancy.