Abstract: Two physical processes of the energy conversion and the current conduction were analyzed in the dynamic process of EBW. According to the characteristics of EBW process, the beam current through workpiece during EBW process was studied using the special multichannel device to collect current signal. The characteristics of the time domain, frequency domain, sequencing, conducting ratio of BCTW were investigated by experimeat. The function between average ratio of BCTW and input electron beam was recognized and peak value of the function was the turning point of the critical penetration state in the dynamic process of EBW.