Abstarct: It is important to study the effects of a contraction in a channel. This phenomenon is specialy produced around bridge piers beside the rivers. Width of a river is usually reduced in a section and then bridge is made there in order to reduce contraction cost. It is important to study the flow and specially flow depth at the contraction section because very narrow section causes choke and channel overflow. To study the effect of contraction on the flow, analytical method can be used which according to this method flow energy before and at contraction sections are equal. It is not possible to compute energy losses with analytical method and therefore it is considered to be zero. In fact there is some energy loss, but because of complicated computations it is not calculated. In this thesis numerical methods are used to model the flow passing a contraction section. The advantage of numerical method is that energy losses is considered. Therefore aim of this study is to model flow numerically and compare it with analytical methods. To compute flow field, Reynolds Averaged Navier-Stokes equations have been used, also to calculate turbulent quantities k- and RSM models and to specify free surface flow, VOF method are used. In this modeling to solve velocity-prssure equations, PISO algorithm is used. To validate the modeling, Aukle (1983) experimental data has been used. The modeling is done by Fluent software and the results has good agreement with experimental data.