Abstract: Stochastic hydraulics is a new development in the research of hydraulics. By coupling a stochastic model with a deterministic model, the computation of unsteady open channel flow is studied. Saint Venant equations are used as the sys -tern model. We use stochastic models for the inputs including roughness, cross-section, hydraulic radius and so on. The outputs of discharge and water level varyingwith time and location are stochastic. An unsteady flow in the downstream ofZhexi Water Power Station is calculated by this method as above, and the resultsare compared with the observed data.