Abstract: Aiming at the difficult problem of unequal assembly gap before welding, which is common in the laser welding process of aviation complex thin-walled components, a study was conducted on adaptive laser welding of 1.2 mm TC4 titanium alloy plates with unequal gaps.A three-dimensional transient thermal-fluid coupling model was established to analyze the impact of different welding gaps. The results indicate that to balance welding quality with the linearly increasing gap width, the laser energy density gradually decreases while matching the corresponding laser spot radius. As the welding gap increases and the laser energy density decreases, the surface tension and recoil pressure on the keyhole inner wall significantly decline, failing to sustain the high-temperature, high-speed Marangoni circulation required for a long conical molten pool. The fluid velocity at the keyhole tip decreases markedly, transforming the keyhole shape from a long conical to a flattened gyroscopic shape, thereby diminishing the strong impact on the molten pool bottom. Consequently, the vortex at the molten pool bottom disappears, and the weld profile transitions from an X-shape at the starting section to a Y-shape at the ending section.