A transfer matrix which transfers the electron states from one side of
the interface to the other is defined for crystalline multilayer with
layers joined coherently. The total transfer matrix for several seque
ntial interfaces can be simply obtained by multiplication of the matri
ces. The bound states as well as the extended states can be naturally
described in terms of transfer matrix. As an illustration of using tra
nsfer matrix, the equation of quantum well states for sandwich structu
re have been given in this way. PACS: 73.20.Dx, 71.10.+x.