Abstract: The microstructure and mechanical properties of deposited metal under different shielded gases were investigated by means of optical microscopy,scanning electron microscopy with EDS,tensile and impact tests. The results indicate that the best mechanical properties of deposited metal with the medium alloy solid wire were acquired when welded with Ar+5%CO₂ mixed gas. The granular bainite dominated the microstructure of the deposited metal,and the existence of fine lath bainite improved the toughness effectively. In addition,carbon obviously enriched in M/A constituents,and massive M/A constituents could cause stress concentration by dislocation pile-up between M/A and base metal. Meanwhile,the micro crack appeared fre-quently at the stage of crack nucleation. The increase of inclusions with large size was the main reason of the appearance of quasi-cleavage fracture and the decrease of impact absorbed energy.