Rare earth elements (REEs) doping technology can effectively control the microstructure and improve the quality and performance of materials. This paper summarizes the research progress of REEs in metal additive manufacturing (MAM) in recent years and briefly introduces the effects of REEs on the molten pool fluidity, purified structure, and interfacial bonding between the molten cladding layer and substrate. It focuses on the mechanism of the role of REEs in the refinement and homogenization of microstructures, including grain growth, columnar to equiaxed transition (CET), and elemental segregation. The reasons for the influence of REEs on the homogenization of the structure and elemental segregation are analyzed. The effects of REE type, content, and dimension on hardness and wear resistance are investigated. Finally, tribological applications of REEs in biological and high-temperature environments are summarized, and the impact of REEs-modified alloys is summarized and prospected.