The invention discloses a welding gun supporting auxiliary device for marine welding operation. The welding gun supporting auxiliary device comprises a welding gun supporting rod, a fixed support, a sliding support, a first fastening bolt, a second fastening bolt, adjustable nut bolts, an adjustable rigid fixing F-shaped clamp and an adjustable flexible fixing F-shaped clamp. A circular smooth rod serves as the welding gun supporting rod. One end of the welding gun supporting rod passes through a circular hole of the fixed support and is fixedly connected with the circular hole, and the other end of the welding gun supporting rod penetrates a supporting rod hole of the sliding support so that the sliding support can move on the welding gun supporting rod in the axial direction. According to the welding gun supporting auxiliary device, by stably controlling the dry elongation of a welding wire, various welding defects such as pores, incomplete penetration, undercut and splashing which are caused when the distance between a welding gun and a welded workpiece is manually controlled and changes in the existing welding process and consequently the dry elongation of the welding wire is not stable are eliminated, and finally weld joints which are stable in fusion depth, smooth in surface, uniform in weld leg size and high in straightness are obtained.