Abstract: The unitary problem between numerical solutions and the analytic solutions is an important issue to value whether or not the physical nature and structure of a numerical method are reasonable in computational electromagnetics. This paper presents the structure functions of T-matrix method based on H-wave incident, boundary conditions of 2D dielectric scattering, and 2D Green's function and extinction theorem. The full analysis of T-matrix's limitation problem shows that when the boundary of a dielectric is limited to the cylindrical one, the limitation transition from the T-matrix solutions to classical ones is obtained.