The invention discloses a welding short section and a welding method, and belongs to the technical field of welding between carbon steels and dissimilar metals. The welding short section has a first connecting end and a second connecting end, wherein the first connecting end is welded with a stainless steel pipe or a double-metal composite steel pipe; the second connecting end is welded with a carbon steel pipe; the inner wall of a carbon steel outer basal pipe is lined with a stainless steel lining pipe, and the stainless steel lining pipe is shorter than the carbon steel outer basal pipe, and extends in a direction from the first connecting end to the second connecting end; one side of the stainless steel lining pipe at the first connecting end is an external end, and the other side in the carbon steel outer basal pipe is an internal end; the inner wall of the carbon steel outer basal pipe and the inner wall of the stainless steel lining pipe is continuously lined with an insulation lining layer which spans two sides of the inner end of the stainless steel lining pipe; and after the carbon steel pipe is in welded connection with the stainless steel pipe or the double-metal composite steel pipe, the insulation lining layer with a certain length is arranged between a stainless steel material and a carbon steel material.