The electron beams generated from the irradiation LINAC which is used for industry irradiation must be scanned. The current in the scanning coil should be quasitriangle wave to make the beams uniformity in the scanning direction. In the system the period of the scanning current is completely synchronized by the major pulse of the modulator in order to avoid the beat. The highest speed of the irradiation bed can be determined by the frequency of modulator, scanning width, and the size of electron beam spot to ensure the high efficient irradiation.