Abstarct: Turbid or gravity flow can be described as entering an apparent mass density of the fluid to a fluid with a different mass density. When the turbidity current of the river flowing into the reservoir behind the dam, due to its heavier weight sinks into the surrounding water, and streams at the bottom of the slope. This phenomenon that is caused by the difference between densities of the fluid laxyers is called density current. The density current containing suspended solid is called turbid current. If the density of the inlet fluid is more than the bulk density of living environment fluid, it will move as a thick underwater dense current With the advent of computers and new strategies for solving partial differential equations of motion of water and sediment, numerous mathematical models with varying degrees of accuracy and simplifying assumptions to simulate the deposition of the Reservoir formed. Due to the difficulty of direct measurement of sediment deposited in reservoirs and high costs, and the inefficacy of the experimental methods for all dams, mathematical models and computer tools are very useful as attention and have been used. In this thesis is to evaluate the application and Flow-3D model to simulate the propagation of turbid stream in the reservoir is studied In this study, the effects of concentration, particle size and flow characteristics such as speed and altitude on the slope sediments accumulated paid. Furthermore, the morphology of the deposits changes in the pattern of investment sediment is considered. The results of the identification of the mutation in the muddy sediments containing fine particles and prediction would be useful in the design The present study was collected in 5 seasons. After the present introduction the second chapter illustrates the genesis of density and turbidity flow theory. In reference to the previous research in the field of density and turbidity currents is generated. The third chapter describes the governing equations for the flow such as equations of continuity, momentum, RNG and k-ɛ turbulence models. Then the different numerical methods to solve the equations used are briefly introduced. And the properties and methods of the software used in this project (Flow- 3D) have been described in detail In the fourth quarter, Flow-3D software with the results of the study were validated by experimentally baas, and after various tests for validation of the model, morphological changes in precipitation patterns were examined and finally, the best and most calibrated numerical model to simulate the propagation of muddy offered that can be used in future research. In the last chapter, the results of the simulations were presented and the conclusions, strengths and weaknesses of the model with suggestions have been expressed