Abstract: In the era of precision medicine, the effectiveness of therapy and diagnosis depends not only on the intrinsic function of drugs or probes but also on their ability to reach specific target sites with high accuracy. Achieving precise molecular localization in vivo becomes a central challenge that limits the further development of many biomedical technologies. DNA nanostructures are programmable nanomaterials constructed from DNA. They exhibit structural precision, favorable biocompatibility, and the capacity for spatial organization of functional units. These features provide a robust material foundation for the development of precise delivery systems. This article systematically describes the fundamental concepts of DNA nanostructures and the principles and strategies of targeted modification. It focuses on the mechanisms by which multilevel targeting can be achieved through molecular recognition tags, regulation of physicochemical properties, and intracellular localization strategies. The potential applications of these systems in disease therapy, diagnostic imaging, and cellular manipulation are also discussed. In addition, current challenges related to stability, biosafety, and large-scale production are analyzed. Future perspectives are proposed with emphasis on the integration of DNA nanotechnology with artificial intelligence and dynamic responsive systems.