Abstarct: Computers have been used to solve fluid flow problems for many years. Numerous programs have been written to solve either specific problems, or specific classes of problems. From the mid-1970's, the complex mathematics required to generalize the algorithms began to be understood, and general purpose CFD solvers were developed. Computational Fluid Dynamics is now an established industrial design tool, helping to reduce design time scales and improve processes throughout the engineering world. CFD provides a cost-effective and accurate alternative to scale model testing, with variations on the simulation being performed quickly, offering obvious advantages. ANSYS CFX is a general purpose Computational Fluid Dynamics (CFD) software suite that combines an advanced solver with powerful pre- and post-processing capabilities. There are a number of different solution methods which are used in CFD codes. The most common, and the one on which CFX is baxsed, is known as the finite volume technique. In this technique, the region of interest is divided into small sub-regions, called control volumes. The equations are discretized and solved iteratively for each control volume. This study presents the results of numerical studies on a three-dimensional free-surface channel flow over a bottom obstacle. Main interest is the capability of commercial CFD codes to solve such problems. ANSYS CFX was used with its built to solve two-phase flow models. The flow field is obtained by the Reynolds Averaged Navier-Stokes (RANS) equations. The dynamics of the turbulence and Reynolds stress is described by turbulent models. Also, The free surface has been simulated by Volume Of Fluid technique (VOF). The boundary conditions which were used to solve these cases, are as following: Symmetric boundary condition Wall boundary condition Inlet boundary condition Outlet boundary condition Openning boundary condition For validation of these models, two sets of experimental results were used. In the first case, which was free surface profile over rectangular broad-crested weir, numerical results were compared with experimental results of MD. Akhtaruzzaman, Sarker and David G. Rhodes. In the second case, free surface profile and velocity vectors were computed for several sections and numerical results were compared with experimental results of M. Salih Kirkgoz, M. Sami Akoz, and A. Alper Oner. The numerical simulation results were entirely consistent with experimental results.