The 3D finite element analysis is used to calculate and analyze the limit load of mitred bend with the longitudinal crack under internal pressure. A finite element model of mitred bend with the longitudinal crack is created, and the influence factors of the limit load under internal pressure are studied. The influence of several dimensionless parameters such as the relative thickness, the relative shapefactor, the relative depth is analyzed. The variation law of the limit load of the longitudinal cracked mitred bend with the shape parameters is summarized. It is found that there is the critical value for each shape parameter. When the parameter exceeds the critical value，the limit load of the structure will decrease significantly.