Abstract: A nanostructured surface layer was fabricated by means of high energy shot peening(HESP) on SS400 steel welded by metal active gas welding process.The refined microstructure in the top surface layer was characterized with transmission electron microscopy, and the residual stress was examined with XRD at the same time.Experimental results show that after the HESP treatment the coarse grains of the surface layer may be refined down into-10 nm scale, and the compressive residual stress on the surface layer be induced.The results of low strain rate tensile experiment of SS400 steel welded joint in solution(Ca(NO₃)₂ 57%+NH₄NO₃ 3%) at 98±3℃ indicate that the resistance of SS400 steel welded joint to stress corrosion cracking(SCC) has been enhanced.The enhancement may be attributed to the combined influences of nanostructured surface layer, compressive residual stress and eliminating micro-defect in welded joint of SS400 steel.