Tidal turbine is a device that converts the kinetic energy of water into electrical energy. Although tidal energy resources are abundant, the energy acquisition efficiency of actual tidal turbines designed by traditional methods is limited due to the Beta theory. A horizontal axis tidal turbine with a lobed ejector was designed to efficiently utilize tidal energy by taking into consideration the effect of the lobed ejector. The optimal Latin hypercube design method (OLHD) was used to extract sample points for the geometric parameters of the lobed ejector. Then response surface methodology was used for the optimal design of the power coefficient, the main index of the hydraulic performance of tidal turbine. The CFD simulation results show that after optimizing the geometric parameters of the lobed ejector, the power coefficient of the turbine increases by 98.88%. Therefore, it is concluded that the proposed horizontal axis tidal turbine with a lobed ejector can be used for the efficient utilization of tidal energy. Optimizing the geometric parameters of the lobed ejector is beneficial to significantly improve the power coefficient of the turbine, and is more conducive to the actual power generation, which has certain engineering significance.