Whether the energy of the electron beam from the irradiation LINAC is stable or not depents on the stability of the operating frequency of the power source. The dispersion and the slight jump of the spectrum of the mabnetron in a short time causes to decrease the controlling accuracy of the frequency stabilization system. Finally, the scanning uniformity of the electron beam descents. The adaptive linear element (ADALINE) and the noise canceling technique are introduced to eliminate the influence of the dispersion and the slight jump of the spectrum on the frequency stability on long time. Thus the scanning uniformity of the electron beam can be assuured.