Abstract: In this study, commercially pure cobalt starting sheet and lifting ear with the same material were welded by resistance spot welding at different welding parameters. The microstructural measurements of welded joints had been investigated metallographically. The influence of several welding steps on the phenomena of parallel slipping bands, cross slipping bands and recrystallization in columnar grains had been analyzed and discussed. The result showed that: when the base metal is pure metal, proper low supercooling on the front of solid/liquid interface and low nucleation make the columnar grain easier to form; the applied electrode pressure during cooling process was mainly responsible for the formation of slip bands in the columnar grains. The larger the electrode pressure, the denser the slip bands; there are uncompleted dynamic recrystallization in the deformed columnar grains, parallel and crossing slip lines take the role of the growth steps of new crystal nucleation and growth.