Abstract: The underreamed structure significantly increases the contact area between the anchor solid and the soil, altering the linear stress transfer path of traditional anchors. This fundamental change in the mechanical mechanism of underreamed anchors greatly enhances their bearing capacity. Future development will focus on technical optimization, standardized construction, and special geological applications. This paper comprehensively analyzes the research progress of underreamed anchors, with emphasis on their structural classification, reinforcement mechanism, calculation theory, and existing research issues. As an effective foundation pit slope reinforcement technique, underreamed anchors substantially improve pullout resistance and play a crucial role in foundation pit stability reinforcement. The paper elucidates shortcomings in understanding their bearing characteristics, pullout failure modes, and the interaction between end resistance and side resistance of the underreamed head. By reviewing and analyzing deficiencies in relevant research, this study provides reference basis for further development and application of underreamed anchor technology. The performance of underreamed anchors is primarily influenced by multiple factors including anchor burial depth, underreamed head diameter, and surrounding soil layer properties. Future research should strengthen and improve the bearing capacity calculation theory of underreamed anchors and optimize construction techniques to promote standardization and normalization of this technology.