Gas pumping-exhaust well is applied more and more widely in coalmine safety production in recent years, but its construction period is long with difficulty. Take the example of serious collapsing accident, analysis was made on the case stress; based on the analysis, the checking calculation method for tri-axial stress of large diameter case was discussed in detail. By the comparative analysis, the tri-axial stress calculation results are more accurate than the ones by traditional uniaxial stress calculation method.