Abstract: The R&D activities concerning electron beam welding (EBW) keyhole dynamics and,EBW mechanism were reviewed briefly in this paper.The character of the depth and formation of the EBW seam was induced in the three typical stages of EB deep penetration processing.The three stages include the beginning stage,the welding stage,and the fade-out stage.Some special dynamic characteristics were disclosed using some special phenomena in the EBW processing,and at the same time,the physical models of the EB deep penetration were put forward.The different function and application of the inner signal which the EB made acting on the metal target and the characteristic and applicational foreground of the outer signal in the dynamic study of EBW were analyzed.The inner signals include the secondary emitted particles,X-ray,the visible light,the infrared rays,the special sound and etc.,and the outer signals are X-ray,the infrared rays,the ultrasonic wave and etc..The relationship between the two kinds of signals and the experimental methods of the EBW keyhole dynamics was analyzed.Moreover,the research trend on EBW mechanism and keyhole dynamics was prospected.