Dissolved oxygen concentration is of significance for the seawater quality, environment and aquatic ecosystems. In recent years, hypoxia has become frequent mainly owing to seawater stratification and eutrophication. This study presents a top-hinged flap wave energy aeration device for producing bubbles and supplying oxygen into the bottom seawater. A series of laboratory experiments and a relatively simple 3-D CFD numerical model were conducted to investigate the hydrodynamic behavior of the device in regular waves. The average variation range of the pitching angle (θa) and the wave energy capture width ratio (CW) were examined with the related parameters, including wave parameters, flap property parameters and equivalent damping coefficient. It is found that the θa value increases and CW decreases with increasing incident wave height. With an increase of incident wave period, the θa and CW values first increase and then decrease. The θa value decreases with an increase in the flap length ratio to width, and the CW value first increases and then decreases. Both the θa and CW values decrease with increasing flap density and equivalent damping coefficient. In addition, the dimensional analysis and least squares methods were used to obtain the prediction formula for θa with an acceptable accuracy.