Abstract: The characteristics of small impulse holes in electron beam weld on sheet metal were described.A "high speed fusion" photographic method,by which the cause of formation of the holes was ascertained,facilitated the visual observation of the filament emission and the behavior of the beam.The authors found that the small holes were induced by and closely related to the impulsive emission from the filament, which was heated directly with industrial AC power source.The appropriate ways and means to suppress the small impulse holes were suggested in this paper.Bimetal machine saw blades have been welded successfully without impulse hole by electron beam with intensive welding parameters.The welding process is stable;the weld is good in quality.By positioning the seam adjacent to the root of saw tooth,we may obtain not only a 95% saving of high speed steel but also a prolonged blade life plus better cutting performance.