Underwater high-precision autonomous navigation is a core enabling technology for ocean exploration and development. The positional error of an inertial navigation system (INS) builds up and diverges with time, requiring outside data to be corrected. As an inherent property of the Earth, the gravity field offers stability, autonomy, and passivity, making it an ideal information source. Consequently, gravity-aided inertial navigation technology holds significant research value. This paper systematically reviews the research progress of four important technologies: trajectory planning, gravity matching algorithms, gravity reference map construction, and gravity field adaptability analysis. It is based on an analysis of the system’s technical architecture and fundamental principles. Mainstream methods, such as multi-source data fusion, gridded interpolation, feature evaluation and matching area extraction, sequential correlation matching, nonlinear filtering, and intelligent path optimization, are comprehensively summarized. Furthermore, common unresolved issues in current technological development are thoroughly examined. Finally, in view of the technical bottlenecks at this stage, future research directions are discussed, aiming to provide theoretical references and technical guidance for the subsequent development of a high-precision, high-reliability, and high-autonomy underwater gravity-aided inertial navigation system (GAINS).