Abstract: A three-dimensional model for rock mass failure is proposed based on the self-locking concept in friction analysis.In case of two-dimensional problems,the model gives the same results as those of Mohr-Coulomb criterion.And the three-dimensional model can be reduced to traditional two-dimensional model if the weak plane is parallel to the middle principal stress and/or the middle stress is equal to the minimum principal stress.The results indicate that the influences of the principal stresses and mechanical parameters of the weak plane on the spatial failure region are remarkable in terms of shape and range,that the spatial failure region becomes smaller as the mechanical parameters increase,and that the weak plane will never fail when some threshold of mechanical parameters is reached,no matter what values of weak plane strike and dip will be.And the spatial failure region becomes smaller with the increased values of the middle and minimum principal stresses.Then,the influence of bottom hole pressure on the failure range of weak plane is analyzed for bore holes in naturally fractured formation,with the help of the local coordinate system.