Dissipating the energy downstream hydraulic structures is the main concern of hydraulic engineers when designing such structure. Many authors examined the dissipation of energy downstream hydraulic structures in the laboratory by using different tools such as stilling basins, blocks, increasing the bed roughness and using pendulum sills. Most authors studied how to dissipate the energy experimentally while few used mathematical models. Mathematical models are less expensive and time consuming than experimental work. In this study, Flow 3D software is used to examine the effect of installing a vertical screen downstream hydraulic structure as an energy dissipater device. In order to verify results of the mathematical model, a comparison between an experiment carried out in a flume in the hydraulic laboratory at Zagazig University and Flow 3D software results, has been carried out. After verification, the mathematical model is used to study the water surface profile and energy dissipation under different flow conditions.