Abstract: The embrittlement of welded joints of Super 304H steel was investigated by means of scanning electron microscopy,energy dispersive spectroscopy,transmission electron microscopy,X-ray diffraction analysis and the impact test.The experimental results indicate that the microstructure of welded joints consists of γ-matrix and precipitated phase.The reason of embrittlement of welded joint is that Cr₂₃C₆ precipitated alone coarse grain boundary and the amount of precipitation are the key factors.After being aged at 650 ℃,there are obvious precipitated Nb(C,N) and Cr₂₃C₆ phases in welded joint,and the amount of precipitate reaches a stable value with the increasing of aging time;the precipitation of Cr₂₃C₆ causes the intergranular embrittlement of welded seam,the impact energy of welded joint reduces rapidly,and the fracture mode turns to intergranular fracture.The toughness of welded joint of Super 304H steel depends on the microstructure of the matrix under welded condition.