Low-temperature impact test on four different kinds of weld metal welded by different technologies of high-current MAG welding was carried out in this paper. The results show that different materials and different welding parameters have different effect on impact energy. As the chemical analysis and observation from the optical microscope show that When welding material contains appropriate C, Si, Ti, fine acicular ferrite forms in it; on the contrary, crisp and thick bainite appears. Compares to acicular ferrite which has an Akv>27J at -27°C and better toughness, bainite has a poor toughness and an Akv<27J. The internal friction experiments show that there are two internal friction peaks - Snoek and SKK. The peak is clear when the microstructure is bainite, on the other side, the microstructure is acicular ferrite.