Abstarct: baxsed on the enormity of the dam building, high volume of used materials and high cost of construction, economic function and the aspects of power supply and water, dam is considered as a strategic building. For this reason dam break is the most important case among of natural or engineering events that this event can cause a major catastrophe with destructive fatality and financial losses. In addition to the complexity inherent of dam break flow, existence of obstacles and buildings, changes the rapid variation of downstream flow pattern that make the problem more complex. Therefore all of researchers and engineers effort is studying the comprehensive of this phenomenon and limiting the dimension of the damage caused by it. Hence the aim of this thesis is study the ability and efficiency of the Smoothed Particle Hydrodynamics (SPH) in modeling the dam break against the obstacles. Smoothed Particle Hydrodynamics is a lagrangian mesh free method in which each particle moves according to the property of the surrounding flow and governing equations and carries the properties of water such as density, pressure and mass. This method is used in a lot of fields of engineering, such as solids mechanics, hydraulics and astrophysics. Because of the lagrangian nature, SPH is very suitable for very large and discrete deformations. In this thesis, in order to validation and verify the accuracy of SPH, some two dimensional modeling of dam break against the various obstacles done by SPH; due to limited shapes of obstacles in SPH, modeling of dam break in two and three dimensional case, require changes in the SPHysics numerical code to build different shapes of obstacles against the dam break flow. This changes in code are given in the appendix of this thesis. By comparing the two dimensional modeling results with available experimental data, it is shown that SPH has a good performance and the results have sufficiently accurate. This thesis aims to provide appropriate way to reduce the damage caused by dam break till in the event of dam break accident, be able to minimize the severity of damages by reduce force and velocity of the flow. In order to achieve this goal, first by using a three dimensional dam break model against a single column, the exerted force on column is calculated; the applied force on the column, is calculated with the written numerical code in the appendix of this thesis and by comparing the results with experimental data the accuracy of the SPH method is evaluated. In the following the effect of three parameters: the shape, distance and arrangement style of the obstacles is examined on the flow motion and the exerted force on the obstacles. First by comparing the effect of three obstacle, cylindrical and square and the located square column obstacles in the flow path with the angel, the effect of obstacle shape is evaluated and determined that the shape of obstacle has a significant effect on the flow velocity and the process of formation of the reflection wave. Finally by flow modeling against three obstacle with different arrangement styles and distances between them, the impact of these two parameters is evaluated on the flow velocity and exerted force on the obstacles. The results show that the effect of arrangement style of obstacles on the exerted force is much greater than the distance between the obstacles.