The invention relates to a novel section welding process by using Ar-rich mixed gas for the runners of a real machine, which can effectively achieve re-control of stress field of the runners of a real machine by changing original welding sequence and direction, sequence of welding layers and control of sections and section length to reduce the stress of connection welding seams of water inlet edge and outlet edge of a blade, a upper crown and a lower ring and hazardous areas adjacent thereto or even to change the tensile stress into compressive stress, thus controlling crack of the runners and improving the service life of a set. The result has very high application value on the engineering and far-reaching social significance.