Abstract: Digital twin technology has attracted extensive attention owing to its unique advantages in intelligent manufacturing. In-depth research and widespread applications have been carried out on its conceptual models, theoretical frameworks and practical deployment. As an intelligent manufacturing technology, metal additive manufacturing has seen growing research interest in digital twins. Serving as a bridge connecting the physical and digital worlds, digital twins integrate multi-physics simulation, Internet of Things perception, artificial intelligence and big data analytics to construct virtual models that precisely map physical entities. This enables real-time monitoring of the production process of metal additive manufacturing, as well as accurate regulation and closed-loop optimization of the entire workflow covering materials, processes and structures. This paper systematically reviews existing applications and technical systems from four aspects: the adaptability between digital twin technology and metal additive manufacturing, core application scenarios of digital twins in this field, major challenges in current research, and future development trends. It aims to clarify the technical roadmap for researchers and engineers engaged in metal additive manufacturing and digital twins, and provide references for subsequent studies.