The Darrieus-Savonius hybrid wind turbines are widely used in fields because of the combination of high efficiency of the Darrieus rotor at running conditions and high shaft torque of the Savonius rotor at a starting condition. However, the co-spinning of the Savonius rotor at the running conditions causes the deterioration of mechanical efficiency in wind power generation. In this work, the CFD investigations are presented to illustrate the improvement in mechanical performance of a Darrieus-Savonius hybrid wind turbine by using an opening/closing mechanism of a Savonius rotor, which yields the equivalent system of removal of the Savonius rotor at the running conditions. It is found that the mean power coefficient of the Darrieus-Savonius hybrid wind turbine with the opening/closing mechanism increases comparatively by 69.01% of the hybrid wind turbine without the opening/closing mechanism (a conventional hybrid wind turbine) over the operating range of tip speed ratio where the Savonius rotor is capable of closing itself at running conditions.