Savonius wind rotors with a vertical axis are not much preferred and used due to their lower aerodynamic performance than that of the other high-speed wind rotors. The present study is intended to increase the rotor performance of the Savonius wind rotor with theoretical method by focusing on a curtain arrangement as a wind deflector with a simple construction, which has been designed to increase the performance of the Savonius wind rotor. This curtain arrangement has been placed in front of the rotor so as to prevent the negative torque that occurs on the convex surface of the Savonius wind rotor and causes the performance of the rotor to be low. Thus, it has become possible to make a more efficient use of the wind energy increasing the low performance level of the Savonius wind rotors.