Abstract: The microstructure and mechanical properties of the welding joints of bogie frame were studied through mechanical tests,optical and electron microscope observations as well as electron probe analysis etc.,then the microstructure state and variation of mechanical properties were determined. The results showed that the welded seam gotten from (Ar+CO2) gas shielded arc welding mainly contains proeutectoid ferrite,acicular ferrite and pearlite,while the heat-affected zone of which mainly contains proeutectoid ferrite,perlite and granular bainite. Tensile and impact tests combined with the hardness measurements demonstrated that the corresponding welded joints have favorable mechanical properties.