The microstructure and properties of the butt joint of repair welding of 6 mm 6005 A-T6 aluminum alloy plate for railway vehicle are studied by using the rapid thermal start-up technology（RTS）. The results show that the microstructure of the original welds are dendritic crystal and equiaxial dendritic crystal,the grains are fine,and the microstructure of the weld is composed of α-Al matrix and Mg2 Si,Al0.7 Fe3 Si0.3 second phase;the original weld is affected by the weld thermal cycle of repair welding,the α-Al matrix grains begin to coarsening,and the microstructure deterioration and grain coarsening of the original weld are more serious after three times of repair welding,and more equilibrium phase precipitates out. At the common boundary of the repair welding weld and original weld,as the times of repair welding increases,the grain coarsening is more obvious and the microstructure of interface tends to deteriorate;Using once RTS（80 ℃） repair welding technology before welding,it can be more obvious to reduce the pores caused by the normal repair welding,and at the common boundary of repair welding weld and original weld,the grain coarsening is not obvious,its microstructure is superior to that of once normal repair welding. There are obvious softening zones in as-welded joint and repair welded joint,the minimum HV0.1 hardness value appears in the heat-affected zone of the original welded joint. The tensile specimens of repair welding joints break at 45°,and the fracture has obvious dimple,which is a typical ductile fracture. The strength coefficient of the original joint and the once repair welding joint by RTS is 0.6,and except the welded joint after three times repair welding,when the bending angle of welded joint is 180°,bending specimens have no cracks,and the plasticity of welded joint is good.