The relationships between strength matching and diffusion hydrogen in weld metal were reviewed. The results show that the main sources of hydrogen in the welds of common welding methods are the moisture in welding consumables,impurities in groove and water vapor around arc. Among the influencing factors of hydrogen in weld,the GMAW method has the lowest diffusive hydrogen content,and the metallurgical reaction of hydrogen removal in arc depends on welding method,and the role of auxiliary hydrogen removal process can not be underestimated. When high strength steel is welded with low strength matching weld,the hydrogen-rich zone formed by HAZ is the weak link of the joint; when high strength matching weld is adopted,the hydrogen-rich zone of HAZ is not significant,but the hydrogen content in the weld is high,which becomes the weak link of the joint. The engineering applications of three kinds of relationships between strength matching and diffusion hydrogen in weld metal have achieved satisfactory engineering quality.In the welding of martensitic heat-resistant steel and its dissimilar steel,the innovative theory of high strength matching weld preventing HAZ from forming hydrogen-rich zone needs to be further studied.