Used of finite element software, based on the material characteristic and node semi-rigid experimentations, the model with material multi-linear kinematic hardening and node semi-rigid was established to simulate the test model of coupler steel tube falsework. According to the measured data of the defect, to analyze the nonlinear stability of the model by methods of the consistent defect mode and stochastic defect, the results indicate that the model’s correctness and consistent mode imperfection method’s in analyzing coupler steel tube falsework is feasible, and the structure is a defect-sensitive structure. The brittleness failure characteristic of coupler steel tube falsework was validated and several effective conclusions were educed after comparative study on the deformation mode and load-displacement curve of the test, consistent defect mode method and stochastic defect method.