When two-dimensional extended Kantorovich method is introduced to three-dimensional ex?tended Kantorovich method, a large number of numerical examples reveals a new phenomenon: if the simple three-dimensional extended Kantorovich method is used, the numerical difficulty of iteration non-convergence will occur. Qualitative analysis on this numerical phenomenon indicates that three-dimensional extended Kantorovich method is not a simple introduction of two-dimensional extended Kantorovich method, and they are different in nature.