Today, flood management is one of the most important topics in river engineering due to reducing the fatality and damages caused by it. Several hydrodynamic models including 1D, 2D, 3D and couple hydraulic models have been developed in the world. One dimensional models have a short computation time and only compute the hydraulic parameters of main river channel. They provide no details about inflow or overbank flow and flow changing between river and floodplainds. Dez river in Khuzestan province (Case study) is surrounded by wide low elevation plains. Since the elevation of floodplains is lower than the main channel, when overbank flow occurs, two flows with different velocities and depths should be considered in the main channel and floodplains. In the present study three different modeling including: 1D simulation using existing cross sections, quasi 2D simulation using LINK CHANNELS, 1D-2D modeling with MIKE FLOOD, were investigated. The results indicate the quasi 2D model, despite of the limited computational time than 1D-2D model, has an acceptable accuracy in predicting discharge, water level, inflow and overbank flow simulation and reduction in inundation volume, which is compatible with the fact of inundation volume storing in the floodplains and it can separately compute hydraulic parameters of main river and floodplains. In contrast, there is no possibility for 1D model with the original cross sections to simulate overbank flow, discharge and flood volume reduction. It provides the average of hydraulic parameters throughout the whole cross setions. Moreover, flood routing is imposibe to be investigated in this model.