Swarms of maritime USV(unmanned surface vehicle), as a core technology driving the development of marine intelligence, demonstrate significant application value in military reconnaissance, environmental monitoring, maritime search and rescue, and related fields. However, the inherent characteristics of the marine environment, including highly dynamic conditions, environmental uncertainties, and communication constraints, pose formidable challenges to achieving high-performance swarm control in maritime USV. To address these challenges, recent research advances in this field were systematically reviewed. The characteristics of the marine environment were described, the domestic and international developments in USV were summarized, and the core control requirements and key challenges in complex marine scenarios were analyzed. Furthermore, a comprehensive survey of three representative swarm control methodologies was presented: trajectory-based guidance control, path-based guidance control, and target-based guidance control. Finally, promising research directions and future development trends in maritime USV swarm control are discussed and proposed.