Abstract: Three-bladed Savonius wind turbines are investigated in this paper in order to obtain a relatively smooth and non-negative starting torque. The starting ability and output power characteristics of two-bladed and three-bladed Savonius wind turbines are compared firstly,and the overlap ratio is studied as one of the important structural parameters. The overlap ratio and net overlap ratio of the three-blade Savonius wind turbine are defined according to its structural characteristics. Nine groups of different net overlap ratios are set,ranging from 0 to 0.36（overlap ratio range from 0.14 to 0.50）. The effect of overlap ratio on the starting torque and output power performance of the Savonius wind turbine at different wind speeds are investigated by using numerical simulations and wind tunnel tests.The results show that the reverse starting torque can be eliminated and the starting performance can be improved by setting the net overlap ratio,with a 147.06% maximum increase of average starting torque factor. The output power of wind turbine can be improved when the net overlap ratio is in the range of 0.06-0.11.