The invention relates to a real-time monitoring and detection method for penetration and forming during deep fusion welding for an electron beam. Based on the law of total electron beam current and back penetration beam current relationship, the monitoring and detection method forms a criterion through the research to the law to monitor the deep fusion welding for the electron beam in real time. The real-time monitoring and detection method comprises the steps: setting welding parameters such as an electron beam current Iw, etc., and conducting welding; in the welding process, collecting real-time penetration beam currents I1, I2 and Ic through a beam current sensing and collecting module; according to a penetration current ratio Ro=Ic/Iw, calculating the penetration current ratio Ro; displaying the penetration beam current Ic measured in real time and the calculated penetration current ratio Ro on a computer. Through the monitoring method, process parameters can be adjusted, therefore a high-quality weld seam is obtained, and the efficiency is improved in the mass welding process. In the process of dynamic welding, through the criterion of the penetration current ratio, the site with welding defects on a welding plate can be found in real time, but the welding defects are unable to be seen by the naked eye on the welding plate generally.