In recent years, robotic additive manufacturing technology demonstrated significant potential in fabricating aerospace lightweight structures, characterized by its high efficiency, expansive scale, and mobility. This paper systematically reviews the research progress in aerospace lightweight structures, starting from the demands of manufacturing and repair, and discusses the research background and importance of lightweight technology. In terms of the additive manufacturing technology, a detailed introduction to the design and fabrication of lightweight structures, materials, and functional integration is provided. The key technologies of robotic additive manufacturing are analyzed in depth, including technical characteristics, typical process principles, robot mechanism, equipment, and process planning; the critical challenges of robotic additive manufacturing technology for lightweight structures are also discussed. Finally, future research directions are outlined based on the current technological development status, including multi-process hybrid manufacturing, intelligent monitoring & control, and digital twin technologies, as well as the potential of human–machine collaborative additive manufacturing. This paper aims to provide a comprehensive and cutting-edge scientific view of the research and development of aerospace lightweight structures from the perspective of robotic additive manufacturing, and provides references for promoting the development of this area.