Abstract: S355J2G3 steel plates for high-speed train bogie were welded by Ar rich CO₂ gas shielded welding. The burning loss and transition law of C,Si,Mn and Nb elements in welding wire were analyzed. Furthermore,the effects of the C,Si,Mn and Nb elements in welding wire on the mechanical properties of the weld metal were researched. The experimental results show that the burning loss of Mn and Si will happen during the Ar rich CO₂ gas shielded welding process,and the welded joint properties matched with the base metal can be obtained by increasing the Mn and Si contents in the welding wire. The burning loss rule of C relates to the original contents of all elements in the welding wire. With the increase of the C,Si and Mn contents in the welding wire,the strength of the weld metal increases,and the elongation of the weld metal decreases. The addition of Nb can improve the strength of the weld metal significantly but deteriorate its plasticity and impact toughness,and so the Nb content in the welding wire should be controlled strictly.