In terms of frequency occurrence, Floods account for approximately 40% of all natural disasters around the world, which every year threatens the lives and property of many inhabitants of the Residents riverbank. In most cases, these areas are part of the floodplains, and the most important reason for their productivity is the frequency of floods most of the time, which suitable for farming and other human activities. Flood damage estimation is essential for economic analysis of flood control programs in urban areas, and reliable flood damage models play an important role in the design and selection of flood risk management projects. Therefore, in this research, it Has been studied the structure and content damages, agricultural losses and potential life loss caused by the flood with different return periods and floods in 2007 with the HEC-FIA (Flood Impacts Assessment model) model in the reach of Marbor River, near Semirom city in Isfahan province. In order to provide damaging river reach, at first, cross sections were plotted using the HEC-GeoRAS extention in the ArcGIS environment by the Triangulated irregular network model with high resolution and then the river morphology was entered the HEC-RAS software and roughness coefficients were assigned to each section. On the other hand, hydrological data including discharge data with different return periods, which were obtained from the results of a frequency analysis of instantaneous peak flow data, along with the hydrograph data of the 2007 flood in order to simulate a steady and unsteady flow were entered in HEC-RAS software and the results were proceeded in the form of time series in the HEC-DSS format (RAS storage format) as well as depth grids, arrival time grids and duration grids after post-processing by HEC-GEORAS. Finally, this information, along with a land use map, depth-damage functions, and inventory and agricultural economic information which prepared by local questionnaires and local documents, entered to the HEC-FIA model to assess the economic damage of flood in each sector. The results of the total damage assessment in the Structure Inventories and agriculture sectors for the return periods of 2, 5, 10, 25, 50, 100, 200, 500, 1000 years respectively are equal to 15/21, 34/71, 62/68, 80/55, 107/70, 138/25, 159/65, 190/45, 217/78 billion Rials. The damage caused by the floods in 2007 was also estimated by 14/65 billion Rial in the construction sector. It affects 83/64 hectares of riverbank land and injures damage amount to 15/02 billion Rial to the crops. The results of this study show short return periods have flood led to significant damage, indicates the area susceptibility to flood events and Invasion to the river's riparian. Keywords : HEC-RAS, HEC-GeoRAS, flood zoning, steady flow, unsteady flow, HEC-DSS