Abstract: Conventional welding techniques such as submerged arc welding and gas-shielded welding are constrained by their own equipment limitations, making it difficult to adapt to increasingly complex welding structures. Welding of thick plates, thick-walled pipes, and other structural components of the underwater unmanned device bring challenges. To address this engineering issue, based on the existing research on narrow-gap welding, a hybrid welding method combining narrow-gap oscillating tungsten inert gas (TIG) welding and melt inert-gas (MIG) welding has been proposed to achieve high-efficiency welding of such structures. In this study, the influences of TIG current, side wall residence time, lateral oscillation speed and wire gap distance on the formation quality of narrow gap welds through are investigated through overlay welding tests. The results show that lateral oscillation speed has the least influence on formation quality of weld seam.As the TIG current increases, both the bottom penetration depth, sidewall penetration depth and surface concavity of the weld increase first and then decrease. When the TIG current is 170 A, the values of the three parameters are the highest. When the wire gap is relative low, the interaction between the arcs is strong, resulting in larger wrinkles on the weld surface. Combining the symmetry of the weld cross-section and the formation, the optimal wire gap is 11 mm. The surface concavity increases with the increase of the side wall residence time,there is on obvious variation pattern in bottom and sidewall penetration depth.