Abstract: The technology of underlaying granular flux with different shapes of metal meshes has an important influence on the formation of ultra-narrow-gap weld. The ultra-narrow-gap welding was carried out using the technology of underlaying granular flux with three kinds of metal meshes with "V","U" and "semicircular" structures,respectively. According to the obtained morphology of cross section of ultra-narrow-gap weld,the influence of underlaying granular flux with different shapes of metal meshes on the formation of ultra-narrow-gap weld was analyzed, and then the mechanism of underlaying granular flux with metal mesh preventing arc from discontinuous burning was also clarified. The results indicate that with the increase of surface area covered by granular flux below the sidewalls,the constricting action from melting flux cooling arc could be enhanced and constricting angle of arc α decreased,which led to the decrease of melting height on sidewalls. If melting height was lower than the filled height of melted wire,a convex weld would be produced. Underlaying granular flux with metal mesh could benefit to form cathode spot rapidly on the surface of workpiece and increase the melting of granular flux,which could make the travel speed of cathode zone be equal to that of wire tip along the horizontal direction, consequently,the arc column would not be stretched and the arc could burn continuously and steadily.