Abstract: An investigation into the influence of niobium on the hydrogen cracking suceptibility and mierostructure of manual metal are weld metal has been carried out by means of G-BOP(gap bead-on-plate) test.It was fourd that,in general,with the increasc of niobium content the cracking susceplibility of weld metal increased gradually,but with riotium content below 0.03% the cracking endency was rot observed.Loweting the hydrogen content of weld metal resuled in a significant decrease in cracling,but this effect was less prorouncedwith increased niobium.Niobium promoted the formation of ferrite with second phases (FS) and suppressed the growth of grain boundary ferrite (GF),probably by niobium carbide precipitation at the interface between the austenite and newly formed GF.The expression for the relation between hydrogen cracking susceptibility and niobium content of the weld metal,including some other welding parameters,has been established.