This study aims to predict the bed elevation change of river and reservoir by compound water model, two-dimensional jet model and one-dimensional density current model, assuming that the river has a single channel and the reservoir has multiple channels. In numerical model, discharge and water level changes is obtained by flow continuity equation and flow momentum equation through double-sweep method, and then applied to sediment continuity equation to predict the scour and deposit of channel bed. The span ranged from the Bosung Dam to Mundueok Bridge at the upstream of Juam Dam, which is approximately 31km long (13km of river and 18km of reservoir), is taken as survey area.