Abstract: This article deals with the brittle failure of duplex stainless steel 00Cr25Ni7Mo4N occurred during intergranular corrosion test.The embrittlement mechanism was studied with metallographic examination,scanning electron microscope and transmission electron microscope.The results showed that R phase and Fe3Cr3Mo2Si2 phase precipitated during sensitization heat treatment in 00Cr25Ni7Mo4N,which resulted in embrittlement and a worse impact toughness for 00Cr25Ni7Mo4N.The requirements of service conditions for 00Cr25Ni7Mo4N after hot working processes were given in the end.