Surface-functionalized magnetic iron oxide (F-Fe 3O 4) nanoparticles are receiving considerable research interest due to their exceptional chemical stability, strong magnetic responsiveness, and excellent biocompatibility. At present, F-Fe 3O 4 nanoparticles are widely used in many fields, including interfacial separation, catalysis, biosensing, and medical Nuclear magnetic resonance imaging. However, there are still cognitive blind spots regarding the application of F-Fe 3O 4 nanoparticles in different fields. Herein, first of all, the basic theories of magnetic Fe 3O 4 nanoparticles were systematically discussed, including structural characteristics, magnetic behavior, preparation methods, and characterization techniques. Then, based on the fundamental theories, the applications of F-Fe 3O 4 nanoparticles in important fields (such as oil-water interface separation, photocatalysis, thermal catalysis and electrocatalysis, biosensing and medical magnetic resonance imaging) were systematically reviewed. Finally, the paper delves into the scientific challenges faced by F-Fe 3O 4 nanoparticles in various application fields, thereby providing potential insights and directions for the further development of F-Fe 3O 4 nanoparticles. This review is helpful to deepen the understanding of the scientific issues faced by F-Fe 3O 4 nanoparticles and provide theoretical guidance for the development and application of F-Fe 3O 4 nanoparticles. Additionally, this review provides the necessary engineering theoretical guidance to accelerate the large-scale commercial application of F-Fe 3O 4 nanoparticles, which possess significant scientific value and profound social significance.