Abstract: Phase structure characteristics nearby the interface of Fe₃Al/Q235 diffusion welding are researched by X-ray diffraction (XRD) and transmission electronic microscope (TEM),etc.The test results indicated that obviously diffusion transition zone forms nearby the interface of Fe₃Al/Q235 under the condition of heating temperature 1 050~1 080℃,holding time 60 min and pressure 9.8 MPa,which indicated that the diffusion interface of Fe₃AVQ235 was combined well.The diffusion transition zone consists of Fe₃Al and α Fe(Al) solid solution.Microhardness in the diffusion transition zone nearby is HM 480~540.There is not brittle phase of high hardness in the interface transition zone.This is favorable to enhance toughness of Fe₃Al/Q235 diffusion welded joint.There is crystal oriental relation of (111-0)_α-Fe(Al)//(011)_Fe3Al和001_α-Fe(Al)//100_Fe3(Al) between Fe₃Al phase and α Fe(Al) solid solution in the diffusion transition zone.