Tidal supercharger is an important device of direct coupled tidal energy and seawater reverse osmosis system. It is mainly consisting of three parts: hydraulic turbine, gearbox, and hydraulic pump. The tidal supercharger is directly driven by the tidal energy and output high-pressure seawater for seawater reverse osmosis process. A novel tidal supercharger was experimentally studied in this paper. It was found that increasing the work seawater flow rate is helpful for improving the input power and output power of tidal supercharger. More output power is required for tidal supercharger as a higher pressure of high-pressure seawater is needed for the RO process. The high-pressure seawater flow rate increases with increasing work seawater flow rate, and high-pressure seawater flow rate decreases when a higher operation pressure is needed for RO process. The efficiency of tidal supercharger increases with increasing work seawater flow rate.