Abstarct: Modern exploration seismology has been developing very fast as a result of the growing need to provide new energy resources and to exploit the existing ones more efficiently. Definition of an accurate velocity model is one of the most critical steps for successful imaging of the subsurface. Seismic tomography is one of methods that provides a velocity model of the subsurface of the earth using seismic data. Today this method is applied in many fields in the large scale crustal studies to engineering problems with multiple dimensions. This method can be used in completion of drilling data and geological interpretation of semi-complex areas and to determine the distribution of pores and fractures and precise determination of the weak (low velocity) and strong (high velocity) formations. In this study using seismic tomography for careful review of existing structures and fractures in Khersan 3 Dam region. The aim of seismic tomography in this region is to detect potential flow and transport paths in mass rocks. Finally, the seismic tomography has clearly identified structures and low velocity areas that correspond with the weaker zones and high velocity areas that correspond with the more compact zones. Revealing the weak zones, in the later stages corrective actions to improve the situation in these areas will be conducted. To achieve the desired targets, four lines of P-wave seismic tomography data in right abutment and floor of Khersan 3 Dam has been used. From results of selected data, first arrival times are obtained. This arrival times read in Geo Tomo software. In direct modeling, the initial model is defined on the basis of geological and geophysical data. This model represents an initial guess of the subsurface structure is baxsed on existing conditions. After ray tracing by software, inversion processes is performed. Results are two-dimensional and three-dimensional seismic velocity model of the four studies areas. With studies these models, laxyers of Earth's Condition in right abutment and floor of Khersan 3 Dam basin is characterized. Show models on topography of the area, display positions and areas of high and low speed zones in abutment and floor of dam with better resolution than previously indicated.