Abstract: The corrosion properties of base metal and welding joint of ultra-pure ferritic stainless steel containing tin were studied by pulsed tungsten argon arc welding technique. The result showed that the corrosion properties of the weld was equal to that of the base mental. By adding Ti and Nb which formed the second phase Ti(C,N) and Nb(C,N), the unmelted Ti(C,N) and Nb(C,N) played a important role in refining ferritic grain and strengthening second phase during the welding thermal cycle. Simultaneous, the corrosion properties of the base metal and the weld were both improved by adding microalloy element of Sn, due to the segregation competitive mechanism between Sn with formed Ti(C,N) and Nb(C,N).