By using the mathematical uniform design, a new agglomerated flux for high speed and multi-arc submerged arc welding (SAW) has been developed in this paper, which performs excellently in welding process, and the effects of flux composition on the welding characteristics is analyzed as well. The mechanical tests show that the weld metal obtained in SAW with this flux exhibits high toughness at low temperature, and the other mechanical properties of the weld metal also satisfy the technical specifications for the West to East Pipeline Project in China. The microstructures of the weld metal are also examined. Both optical and TEM microphotoes demonstrate that the weld consists mainly of small-sized and uniformly distributed acicular ferrite. These microstructures can effectively prevent the initiation and propagation of micro cracks, resulting in high notch toughness of the weld metal at low temperature.