The invention discloses a submerged-arc welding method for low-carbon Q420qNH weathering resistant steel for a bridge and belongs to the technical field of welding of bridge steel medium-thick plates.The submerged-arc welding method comprises the specific steps that (1) a double-face V-shaped symmetrical groove is formed in double-butt-joint parent metal of a base material; (2) the V-shaped symmetrical groove and the two sides of the V-shaped symmetrical groove are polished and cleaned; and (3) submerged-arc welding is conducted. Through the welding technology, multi-pass continuous submerged-arc welding is achieved without weld preheating, postweld heat treatment and gas shielded arc welding priming in the welding process, an obtained welding joint is excellent in structure and mechanical performance, a simple, efficient and economical welding mode is achieved in the manufacturing process of a novel Q420qNH weathering resistant steel medium-thick plate structure for the bridge, and vital significance is achieved for facilitating popularization of the novel low-carbon weathering resistant bridge steel.