Abstract: The plasma wave nonlinear effect of IonChannel Electron Cyclotron Maser (ICECM) is investigated. Using these methods of fluid theory and self nonlinear theory, the micromechanism in ICECM are analyzed. Studies find that the longitudinal focus is intensified and the beamwave interact efficiency is remarkably increased. Numerical calculations show that , for middle ion density and the electron beam of 1.5kA and 1MV, the scattering wave frequency and the output power in ICECM system can achieve 280GHz and 200MW respectively.