The welding quality of nuclear island primary pipes is one critical point of quality control for nuclear power plant construction. The article introduced the narrow gap automatic welding technology and the quality control measure of this welding technology, based on a welding project for primary pipes of nuclear power plant in China. The results of this project’s product quality inspection show that the narrow gap automatic welding technology is feasible for primary pipes, the quality control measure is effective, and the quality of product’s appearance and inherent meets the design requirements. The experience of this quality control measure can be used as a reference for similar engineering construction.