Abstract: Invar steel has an extremely low coefficient of thermal expansion, making it widely used in the manufacturing of molds for aerospace composite materials. Most existing studies focus on process aspects, lacking in-depth analysis of the fluid dynamics behavior of the molten pool. Therefore, numerical simulation and high-speed photography were employed to analyze the effects of different process parameters on the molten pool morphology evolution and arc characteristics during laser-TIG hybrid welding of Invar steel, which provides crucial theoretical support for the optimization of the Invar steel welding process. The results indicate that within the laser power range of 5 ~ 6 kW, the increased power leads to greater recoil pressure, which promotes a larger penetration depth and keyhole dimension, intensifies the overall molten pool flow, and makes the arc prone to being attracted by the laser and deflected at a high power. Within the welding speed range of 0.5 ~ 0.8 m/min, a higher speed reduces the heat input, leading to a decreased penetration depth and weld width, and an increased flow velocity and cooling rate of the molten pool; additionally, the arc is prone to deformation at a high speed. Within the welding current range of 150 ~ 170 A, the increased current enhances the arc force, promoting the expansion of weld width and intensifying the molten pool convection; furthermore, the arc is more stable at a high current.