Abstract: Underwater acoustic communication (UAC) system is characterized by limited bandwidth and power. Index modulation (IM) technique has shown great potential in improving spectrum efficiency and energy efficiency and reducing system complexity. Therefore, in the past few years, IM technique has been widely used in the UAC systems and attracted widespread attention of scholars at home and abroad. It is expected that IM technique will be a solution with great potential to high-speed UAC system. This paper focuses on the applications of the IM technique in the UAC system. Performance of the IM technique is analyzed, and the research progress is summarized.