In this paper, the development status of on-line monitoring for the electron beam freeform fabrication are introduced, mainly focusing on the monitoring of the molten pool morphology, the temperature field of forming process and the flow field, with emphasis on the monitoring of the molten pool morphology during the manufacture. At the same time, the prospects of on-line monitoring for the electron beam freeform fabrication are presented, (1) online monitoring the signals of electronic and ion; (2) introduce new signals for online monitoring; (3) real-time tracking each layer’s the quality and height of deposit body; (4) multi-signal collaborative online monitoring.