The aerodynamic performance of a National Renewable Energy Laboratory Phase VI horizontal-axis wind turbine (HAWT) equipped with blades characterized by leading-edge suction and blowing was analyzed numerically in three dimensions using computational fluid dynamics. The effects of leading-edge suction and blowing flow control methods on the flow field and aerodynamic characteristics of the HAWT and its performance were compared. The results suggest that leading-edge suction is superior to leading-edge blowing in suppressing the flow separation on the suction side of the turbine blade and improving the turbine aerodynamic characteristics. However, compared with the baseline turbine, the bending moment acting on the rotating blade of the HAWT to which suction or blowing is applied increased. This increment was greater for turbines with leading-edge blowing flow control blades. The effects of different arrangements of suction slots on the performance of the HAWT were analyzed. The results showed that the net wind power coefficient of the HAWT after deducting the energy consumption of the suction control was 45% higher than that of conventional turbines, indicating great potential for practical applications.