Abstract: Reaction phases and interface structures of the diffused layer formed by electron beam brazing of Nb-1Zr alloy and 304 stainless steel were investigated by optical microscope, SEM, and EDS. It is found that two phases of ε-(Fe₂Nb) and σ-(FeCr) were established and two reaction layers were formed in the interdiffused layer of joint. The reaction layer Ⅰ is loose organization formed of the Fe₂Nb, and reaction layer Ⅱ is formed pillar crystal which is composed of laminated Fe₂Nb and FeCr. The reaction layer Ⅰ brings on frailty of joint and creation crack. The strength of joint relates to diffused layer thickness. When diffused layer thickness is 22 μm, the maximum strength of joint is up to 355 MPa at room temperature.