Abstract: The present report summarized the work on the susceptibility to hydrogen embri-ttlement of steel by C.L.M.Cottrol,F.Watkinson and et cetera,utilizing roundnotched tensile test specimens in a chamber filled with high pressure hydrogen.The specific type of Implant test specimen as recommended by ⅢW(round specimen,8mm diam.,40°deg.notch,<0.1mm root radius,0.5mm notch depth) was analyzed and its shortcomings cited.The influence of notch depth on notched tensile strength of steel 15MnVN in the normalized,thermal simulated and welded state was investigated.The authors present in this paper an expression D for the susceptibility of steel to hydrogen induced cracking,as indicated by the difference in reduction of notched tensile strength caused by hydrogen i.e.,D=(σ_NT-σ_Impcr)/(σ_NT)·100%.The authors give also an example of taking the D value as criterion to compare two different postheat procedures and choose the one suitable for making certain welded pressure vessels free from hydrogen induced cracking.