The control of brass welding porosity is studied by adopting a new method of the intermediate transition layer. The weld porosities of brass laser welding under the copper intermediate layer condition and brass general butt laser welding are contrasted and analyzed. The research results reveal that the porosities of weld surface and weld interior are greatly reduced under the condition of the intermediate layer. As the welding speed increases, the porosity decreases gradually. The porosity is almost zero when the welding speed is 2.2 mm/s. When the welding parameters are the same, the porosity of the weld under the intermediate layer condition is barely one third of that in the normal butt laser welding of brass sheet. The mechanical properties of welded joint obtained at the intermediate layer condition is superior to that of welded joint obtained at normal butt laser welding. Under the premise of good weld formation, the effectiveness of the new method of the copper intermediate layer to control the porosity defects of brass laser welding is verified.