Abstract: By means of chemical composition analysis, bead distribution and gap position analysis and microstructure observation and other means, the causes of impact toughness difference between deposited metal of self-made electrode and butt weld were analyzed. The results show that the different fusion ratio of the base material, the differences between the chemical compositions of the deposited metal and the butt joint root weld and the significant effects of reheating and tempering on butt joint root weld result in the obvious differences between the microstructures of the butt joint root weld and the deposited metal and the difference in impact toughness, and that because the weld bead layouts of deposited metal and butt joint weld are different, and the reheat effect of the first weld bead subjected to the subsequent weld bead is different, different organizational distribution characteristics is formed, which is the cause of difference of the impact toughness.