Abstract: A design and analysis procedure for rotor blades is developed based on vortex theory. Based on free wake model, the aerodynamic performances of horizontal axis wind turbine rotor by adding spiroid O winglets and L winglet at the tip of the blade are studied numerically, the vortex location and induced velocity distribution in different conditions are investigated. The results show that the presence of winglet at the tip of the wind turbine blade improves the power coefficient at the design wind speeds, and downwind winglets are superior to upwind ones with respect to optimization of power.