The influence of welding parameters on weld appearance is investigated by experiment in narrow gap laser metal insert gas (MIG) hybrid welding 10 mm low thermal expansion superalloy GH909. The results show that a desirable weld can be obtained by employing a groove of 10° and the root face of 0.7 mm. A faster welding speed would result in a narrower weld width. The defocus plays an important role in the two heat source coupling mechanism and the better parameter to realize laser-arc synergetic effect is 1 mm in experimental conditions. An appropriate increase in welding gap can improve the penetration. A desirable weld profile without any obvious defects can be obtained using optimized welding parameters. Grains adjacent to the heat affected zone (HAZ) are perpendicular to the fusion line. The columnar crystals touch and restrain each other to form a herringbone in the weld center.