The invention discloses a middle assembling robot welding process for a ship. The middle assembling robot welding process comprises the following steps that a, preparation before welding is conducted, specifically, after a workpiece is moved to a welding position, the workpiece is checked; B, after the workpiece is in place, weld joints are positioned, and the welding sequence and the starting point and the ending point of each weld joint are determined; C, the angle of a welding gun is adjusted, the welding gun with a gooseneck part having a bending angle is adopted by the welding gun, reaches the starting points and the ending points of the weld joints, and flat fillet welding and vertical fillet welding are completed; D, after the welding is conducted for a certain time, welding gun cleaning, wire shearing and oil spraying procedures are started, and the welding gun is prevented from being blocked; and e, after the welding of all welding seam robots is completed, the appearance and size of the welding joints need to be detected. In the welding process, electric arc tracking is adopted, and automatic welding of straight angle and vertical fillet weld of the assembly component in the ship is achieved under the cooperative use of a specific robot welding posture, a welding process, a welding sequence and a swing mode.