Abstract: The heat and mass transfer and molten pool flow in single-pass deposition of wire arc additive manufacturing (WAAM) were studied using numerical simulation, and the influence of wire feeding speed on weld bead morphology was analyzed. The results show that when the wire feeding speed is low, the substrate receives more arc heat, the molten pool has deeper penetration and stronger fluidity, and the weld bead width is wide with a low height. As the wire feeding speed increases, the molten metal accumulates upward, and the molten pool volume increases. When the wire feeding speed reaches a certain value, the electromagnetic force and surface tension achieve a dynamic balance, and the molten pool penetration approaches the weld bead height. At higher wire feed speeds, molten pool convection tends to weaken, and penetration becomes shallow. Under the action of surface tension, edge shrinkage of the weld pool leads to weld bead bumps. The simulated single-bead cross-sectional profile agrees well with experimental results and can provide theoretical bases for controlling process parameters in gas tungsten arc welding-based additive manufacturing technology.