Abstract: The relationship between the earthquake faulting and tectonic stress was considered in this paper. The results of earthquake mechanism were reviewed. It shows that the fault plane obtained from the fault plane solution agrees well with the surface break caused by the earthquakes,but the fault plane solution does not give good explanation for the orientation of stress, and that an earthquake may be a complex rupture process and the onset of P waves just reflects the initial state of this process.The Coulomb criterion for rock failure was applied to investigate the earthquake faulting. It shows that the angle between the faulting plane and the greatest principal stress is less than or equal to π/4 in the homogeneous and isotropic materials.the result obtained from the fault plane solution can be regarded as a special case for them,μ= 0, i. e. no friction exists. When the material contains preexisting faults or weakened zones, the angle may be distributed in a wide range. It depends on the fracture parameters of the material, such as So, S_w, μ, μ_w as well the intermediant principal stress. Five basic processes of the stress changes which may cause an earthquake are discussed in this paper.