Abstract: self-shielded flux cored wire is widely used in the field welding and repair. In the field thin-walled pipeline welding, it is of great significance to reduce the heat input of base metal and ensure the welding quality. Therefore, this paper explores the CMT technology of fine diameter self-shielded flux cored wire, which is suitable for thin-walled pipeline welding in the field. The results were shown that the droplet transfer was the mixed transfer mode under different polarity, the mainly mode was the short-circuit transfer. In DCEP (direct current electrode positive), in the stage of peak, the droplet transfer mode is mainly characterized by globular repelled transfer. In DCEN (direct current electrode negative), the droplet transfer mode is mainly projected transfer in the stage of peak. With the increase of welding parameters, the mixing droplet transfer mode has not been changed. At the same time, the explosive welding spatter mainly occurred in the short-circuit stage under DCEN. The exclusion spatter mainly appeared in the peak stage under DCEP.