Abstract: In order to improve the welding efficiency of the Invar alloy thick plate and reduce the deformation after welding, the welding process of a 60° V-groove flat butt joint of 18 mm thick Invar alloy was explored by using metal inert gas (MIG) welding pulse technology. Firstly, the droplet transition and pulse waveform of MIG welding were optimized by the high-speed photographic camera and waveform recorder to ensure that the droplet transition mode was one pulse and one drop. Subsequently, the manual welding test was carried out with the optimized pulse waveform. The results indicate that when the heat input of the weld filling is 1.1 kJ/mm and the welding pass is 8, the weld is well formed and aesthetically pleasing, the deformation of the post-weld angle is only 5°, the warping height from the edge of the test plate to the middle is 1 mm, and the deformation is minimal, which meets the practical application requirements.