Abstract: In this paper, the crack opening displacement values δ_is, saturated of two types of welded joint of 38CrNi3Mo steel have been measured by the multisection method.The effect of structure property and welding process conditions of two types of weld on the δ_is has been also investigated. The results show that the overheated zone of HAZ of a similar metal welded joint is the weakest zone in toughness, and the low toughness is caused by the structural heredity of HAZ. In the uranami weld metal of combined weld, the weakest zone of fracture toughness is near the bond line, and is related with the structure characteristic and carbon diffusion of the dissimilar steel weld. To a certain extent the combined weld process can prevent the structural heredity of weld HAZ from appearing.