Abstract: Electron beam welding experiments of QCrO.8/lCr21Ni5Ti dissimilar butt joint were carried out.The microstruetures, elements distribution and phase composition of the joint were investigated by means of Optical Micrography, EPMA, EDX and XRD.The results showed that the microstructure of joint mostly consists of phase α+ε, and phase α was quantitatively more than phase ε.A few of Cu (ss.Fe) phase formed only in top weld near to copper side and any brittle phase was not generated in the whole weld.The microstructures and bonding status of joint were evidently affected by changing of h_s (i.e.beam offset on steel side), a small quantity of metal QCrO.8 melted down into weld as value of h_s was less, a large difference of microstructures and chemical composition existed in comparison of weld with base metal QCrO.8.With increasing of h_s the microstructure distribution of joint becomes homogeneous gradually, but the bad fusion' s status happened to QCrO.8 side in weld due to unbalanced heat input and rapid heat conduction of QCrO.8.Even if ft, increased in little range, base metal QCrO.8 may not be fusion, which resulted in forming joint of local fusion or lack of fusion.