Abstract: Based on the Vollenweider model,a stochastic eutrophication model was built. The changing process of total phosphorus concentration was regarded as a random process in the model. If the random properties of initial conditions are obtained,the analytical solution as well as the numerical solution can be found. Therefore the model provides the random properties of total phosphorus concentration,such as the mean and variance. The model was calibrated using the results of a rmnitoring program in Geheyan reservoir.