Abstract-Excitation of extraordinarily polarized azimuthal eigen modes by modulated annular electron beam is shown to be characterized by the increase of instability growth rates compared with the case of non-modulated electron beam. Interaction between the modulated beam and azimuthal eigen modes happens in the range of electron cyclotron frequency in waveguides with metal walls, which are partially filled with cold magneto-active plasma. Nonlinear set of differential equations, which describs excitation of these azimuthal modes by an annular electron beam is derived and analyzed numerically. Different scenarios of the beam-plasma interaction depending on relation between azimuthal mode number of the exited waves and periodicity of azimuthal modulation of the beam density, degree and manner of the beams' modulation are studied numerically.