The invention provides a welding gun pose-variable closed geometric component GMAW added material manufacturing method. A closed geometric component consists of multiple layers of single-way thin-wall pieces connected end to end; an angle between the growth direction of a forming layer and a projection thereof on a substrate plane is smaller than and equal to 90 degrees; the method adopts a method for controlling the arc starting and quenching end joint quantity of the forming layer to improve the forming quality in the end-to-end connecting place; in the forming process, a welding gun gesture is adjusted to enable a welding gun to always point to the growth direction of the forming layer; and the generated arc force and plasma current force direction is parallel to the growth direction of the forming layer, so that the improvement of the stability of a molten pool of the forming layer is facilitated, and the large-dip-angle growth of the forming layer is realized. The method effectively overcomes the difficulties of weak forming quality of the end-to-end connecting place of the closed geometric component and low inclined surface forming capacity, is simple in operation, and is easy to realize automation of the GMAW added material manufacturing process.