Effects of the welding inclusions and notches on the dynamic fracture behaviors of low-alloy steels were investigated by tensile test and acoustic emission (AE). The micro-structures and fracture surfaces of the hot-rolled and welded samples were observed by OM and SEM. It was found out the welding inclusions and notches resulted negative impacts on the tensile performances, which were ascribed to the ferrite coarse grains, welding inclusions and the induced stress concentration. No Luders band propagation was in the welds’ yielding processes, since there were less dislocation origins at the coarse grain boundaries and the welding inclusions reduced the dislocations move speed. During the fracture process of welds, there were four groups of AE frequencies, representing three kinds of fracture behaviors: plastic deformation of the welding matrix, fracture of the welding matrix, and fracture or interface detachment of the welding inclusions, which have characteristic distributions in different fracture stages.