Robotic fish will become the next generation of submersibles due to their advantages of high propulsion efficiency, high mobility, excellent environmental compatibility and good load capacity. However, short battery life and high charging costs would be the main obstacles restricting the deployment of robotic fish for long–term ocean monitoring and cruises. The present methods of either using a mother ship or laying cables are very expensive. In order to greatly reduce the cost, a nearby cheap charging station is necessary. In this paper, a comprehensive review of underwater automatic charging methods and systems for robotic fish based on the existing marine renewable energy conversion technology is carried out, including robotic fish underwater docking and charging technology. Based on the review and comparative analysis, a design idea for a novel and feasible system for underwater charging for a school of robotic fish through renewable energy is proposed.