Additive manufacturing technology holds broad prospects in the production of complex metal components for the aerospace industry, owing to its high design flexibility, excellent dimensional accuracy, and streamlined manufacturing process. However, challenges such as limited spatial dimensions, high manufacturing costs, and process uncertainties during prolonged forming restrict the direct additive manufacturing of large-scale components. Modular design combined with segmented manufacturing and welding technology can effectively mitigate these issues, making it a current research focus in this field. This paper systematically elaborates on the unique microstructural characteristics of metal structures produced by additive manufacturing and the associated welding challenges. It summarizes strategies to address these difficulties from the perspectives of alloy composition optimization, welding method innovation, and the application of auxiliary technologies. The principles and process characteristics of commonly used welding methods for additively manufactured structures are introduced in detail, with a focus on the weldability of additively manufactured aluminum alloys, titanium alloys, iron-based alloys, and nickel-based alloys. Furthermore, the progress in engineering applications of welding for aerospace additive manufacturing components is reviewed. Finally, it looks forward to the potential application of artificial intelligence in the field of welding manufacturing.