Aluminum-copper alloy is commonly used in aerospace lightweight structures because it is lightweight and possesses high strength. Laser welding has a high energy density and a small heat-affected zone, making it widely applicable in welding aluminum-copper alloys. However, due to the inherent characteristics of aluminum-copper alloys, problems such as porosity and cracks are prone to occur when using ordinary single-light-source laser welding. This study employs an infrared/blue light composite laser to weld 2A14T6/2A12T4 aluminum-copper alloy and studies the impact of process parameters on weld formation and joint microstructure. The results indicate that as welding heat input increases, weld seam width increases, while stability during welding decreases. When heat input decreases, porosity at the weld seam is reduced, but fusion on both sides of the weld seam becomes insufficient. The best weld forming effect is achieved when the infrared light power is 4500 W, the blue light power is 600 W, and the welding speed is 30 mm/s. The formation of the weld seam starts at the edge, gradually advances toward the center, and finally results in coarse columnar and fine equiaxed crystals. During welding, due to solidification imbalance, a large amount of strip-shaped θ-Al₂Cu precipitates at the grain boundaries.