Abstract: Cold metal transfer(CMT) spot plug welding of Al6061 and bare steel was carried out by using AlSi5 filler metal. Using orthogonal test method to optimize process parameters, the microstructure and mechanical properties of welded joint were investigated with optical microscope, scanning electron microscopy and universal tensile testing machine. The results show that the welded joint between Al6061 and bare steel could obtain satisfied weld appearance and performance using CMT method. The sequence of significance of process parameters was hole size in bare steel sheet, spot welding time and wire feed speed. The results also indicated that the typical spot weldingbrazing joint, which consisted of brazing zone and the welding zone, could be performed; the pore was the main defect in the welded joint; the maximum shear strength of the joint was more than 4 kN with tear fracture.