Abstract: The atom of hydrogen is the lightest and smallest one among elements,it is movable easily.within crystal lattice of metal even at room temperature.Welding hydrogen induced crack(HIC) is a kind of hydrogen damage of metal during welding of high strength low alloy steel.Its occurrence is related to micro structure,residual stress and local hydrogen concentration in weldment.Up to now,unfortunately,there is no way to check the critical local hydrogen concentration in the vicinity of the initiation of HIC.In this paper the mathematical modeling method combined with quantitative implant cold cracking testing is developed to determine the local critical hydrogen concentration based on the local critical stress in the vicinity of the initiation area of HIC,therefore the criterion for HIC is established.According to the criterion the mathematical modeling and prediction of welding HIC are realized.The experiment shows that the modeling and prediction of welding HIC are feasible.