Karkheh River, the third largest river of Iran, is of high importance due to strategic environmental conditions caused by major water and agricultural projects, industrial and urban water supply. Since the probable morphological changes caused by the process of erosion and sedimentation of the river after dam construction and flooding can affect many water utilities such as a ponds, irrigation channels and pumps downstream of the dam, therefore for this purpose in the present study in a specific range of this river between hydrometric stations at the Paye-Pol and Abdolkhan, the process of erosion and sedimentation and some of its features such as changes in geodetic, cross-section shape of river and total sediment load were all examined and simulated using HEC-RAS model. The simulation period of this research was considered 12 years between 2001 to 2013 and after dam construction. The results show that near Karkheh Reservoir Dam, which is upstream studying area the erosion condition of the river is higher but in the middle and lower areas of the river, less erosion can be seen. Furthermore, in the simulation of sediment transport functions Ackres-White, Larsen and Englund-Hansen have offered better results regarding erosion and sedimentation changes of river. Also morphological studies of Karkheh River showed that construction of Reservoir Dam has failed to prevent the displacement of the central axis of Karkheh River. The results of this survey can be a good reference for the condition of Karkheh River and the effects of constructing Reservoir Dam on its condition for various engineering projects, dewatering and water transport.