Abstract: Mixed gas shield welding experiment of Q550D bainite high-strength steel sheets were done respectively by using GHS-60 welding wire with low strength matching and GHS-70 welding wire with high strength matching. The Y-groove crack sensitivity experiment and heat treatment at 520 ℃ for 1.5 h after welding of the welding joints were carried on. The effects of different strength matching welding wires on welding joints properties were evaluated by metallographic analysis, tension test and impact test. The results show that the cold crack could be avoided using GHS-60 welding wire without preheating and using GHS-70 welding wire when preheating temperature surpassed 80 ℃. The mechanical properties of the welding joints for the two strength matching were well, and the heat treatment after welding had on bad effect on the properties of HAZ and base metal, but it decreased the toughness of the weld centre. So low strength matching was advised to use.