Abstract: The microstructures of electron beam(EB) melt-brazed joint of QCr0.8/1Cr21 Ni5Ti was studied by means of optical microscopy,energy dispersive X-ray analysis and electron probe microanalysis.The results indicated the microstructure of welding seam were macro-homogeneous supersaturated solid solution of iron in copper and thin transition layer consisting of α+ε appeared in upper part of melt-brazed interface,which was joint to 1Cr21Ni5Ti soundly.The condition of structure and heat action to form electron beam melt-brazed joint was given.Based on microstructures and the characteristics of electron beam welding,the physical model that decribed formation process of EB melt-brazed joint of QCr0.8/1Cr21Ni5Ti was proposed and formation mechanism of the joint was discussed.The analysis shows formation of EB melt-brazed joint is made up of four steps:formation of molten pool with keyhole,formation of fusion transition layer,formation of braze welding seam,formation of final microstructure.