Abstract: According to the welding characteristics of the key components of shield machine,the welding experiment of Q345D low alloy steel plate with 50 mm in thickness was carried out by arc welding robot to determine the proper automatic welding process. The results show that the use of deep penetration welding and automatic welding can get high quality welded joint with the butt joint gap less than 2 mm and blunt edge in 2-3 mm and small nozzle for backing welding. The automatic welding of the gearbox of shield machine was realized.