Abstract: Twin half-rotating impeller tidal turbine (THITT) is a new type twin impeller tidal turbine. To explore the influence of layout on its energy capture characteristics, the energy efficiency index was defined to mean its energy capture characteristics. XFlow software was used to simulate and analyze the influence of rotating direction and layout parameters on its energy efficiency index, compare and analyze the velocity distribution and blade force change trend of single half-rotating impeller tidal turbine (HRITT) and THITT, and explore the gain mechanism of energy acquisition characteristics of THITT. The results indicate that when the rotating direction of THITT is internal rotation, the energy efficiency index is significantly improved, and the initial installation angle has a greater influence on the energy efficiency index than that of the wheelbase. The output gain of THITT mainly comes from the increase of resistance of downstream blades. When the layout parameters are near optimal, its energy capture characteristics are 22.4% higher than that of HRITT.