Abstract: This paper was aimed at investigating the properties of welded joints of thick-walled pressure vessels fabricated with 14Cr2Ni4MoV low-alloy high strength steel. It's belived that there were liquation cracks and high temperature low-ductility cracks in the weld heat-affected zone adjacent to the fusion line.The said cracks,under certain condition,could induce delay cracks.Mechanical tests showed that this region was the weakest in the welded joint,it was the short life region.