Abstract: In order to realize the on-line monitoring of the electron beam welding process and ensure the quality of weld formation, a space charge signal acquisition and processing system was developed. The system consists of a sensor acquisition module, a signal processing module and a display analysis module. In this study, multiple sets of 6061 aluminum alloy plate butt welding process tests were carried out, and the electric charge of 8 positions directly above the weld pool was collected in real time. The relationship between the characteristics of the charge signal waveform and the quality of the weld forming was analyzed, and the criterion for the quality of the weld was established. The results show that the signal waveform collected by the system can effectively evaluate the stability of the welding process and determine the forming defects such as welding misalignment, incomplete fusion and burn-through in real time.