Abstract: Base on the basic oscillating properties of the frequencies and the displacement modes in the discrete system of the beam with overhang, it is proved that the stiffness matrices of conjugated system of a two-span beam with one cantilever is to be sign-oscillated. Then, the sign interchanges number of the flexural moment modes of a beam with one cantilever are determined. Furthermore, some qualitative propertiesof its displacement modes, rotation modes, moment modes and shearing force mode are given. The basic oscillating properties about two-span and three-span continuous beams having middle pinned are obtained practically in this paper as well.