The square external brush of the external barrel-washing machine consists of three parts. the first part is a barrel-washing opening which is specially designed, cleaning dust, dirt and stain. the second part is made up of special brushes in the shaped of a barrel. washing the barrel body thoroughly. It will remove the stain but will not damage the barrel and printed pattern on the barrel, the third part is made up of special brushes on the bottom of the barrel. It can not only wash barrel with flat barrel, but also barrel with sunken bottom.