Abstract: A stress distribution function of directional well rock wall is set up and the stress distribution of directional well wall surrounding is analyzed through the coordinate transformation system.The collapse pressure and breakdown pressure calculation model of directional well is created based on Mohr-Coulomb strength criterion and the maximum tensile stress rupture criteria.Computational analysis software of directional well for borehole stability is established according to above results.Collapse pressure and breakdown pressure of borehole is determined and the relationship map between collapse pressure and breakdown pressure varies with azimuth of deviation angle is set up obtaining minimization drilling risk along the minimum horizontal principal stress direction.