Abstract: This paper reveals some latent insufficiency of LBB stability analysis, which has been ignored for a long time. DPFAD method overlooks the problem of non-linear loading curve; J-integral tearing modulus inter-section method also overlooks the problem of non-linear J-integral loading curve. Such deficiency detracts from the accuracy of these methods, while the optimization assessment method can gain higher precision than them with no hypothetical or geometric approximation. This paper provides reliability analysis based on different stability analysis theory and calculates the critical crack length of an engineering example as a reverse problem to stability analysis.