On the basis of two-dimension finite element analysis,the two-dimension stress intensity factor correction coefficients of typical lug joint were obtained; Three dimension elastic plastic contact finite element model of the typical lug joint was simulated and analyzed,and the lug thickness correction factor was introduced. Based on the results of two-dimension stress intensity factor correction and three-dimension finite element stress intensity factor simulation,the plug thickness correction factors were fitted,then get the expression of stress intensity factor of three-dimension model ofⅠtype crack in typical lug joint.Finally the corresponding stress intensity factor expression was carried out to verify the accuracy,which combined with the corresponding residual strength test. The results show that the stress intensity factor calculation formula is accurate.