Abstract: Macro-analysis,metallographic analysis,scanning electron microscopy (SEM),energy dispersive X-ray analysis (EDAX) and chemical composition analysis were adopted to study the reason for early cracking failure of the welded seam for stainless steel radiating pipe in a diesel engine.The results show that the early cracking caused by stress corrosion.The early failure was mainly attributed to improper welding technique and inappropriate welding electrode,which formed the crack source because of decreased strength in the joint zone.The existance of Cl- in cooling water might be the enviromnental reason for SCC to occur.