We used the focal mechanism of crustal earthquakes to estimate the magnitude and direction of the maximum principal stress near Tehran. Our assumptions are that the slip vector lies in the fault plane and is parallel to the maximum resolved shear stress in that plane. The theoretical analysis is tested using accurately determined focal mechanisms of 51 earthquakes) that occurred along the Mosha fault. The earthquake focal mechanisms in the Central Alborz are divided into seven groups with respect to their location. The method that applied here is based on a developed stress inversion of Michael proposed by Vaclav Vavrycukin 2014 by applying the fault instability constraint and the stress is calculated by iterations