Horizontal axis wind turbines are now prevalent across the world for wind energy harvesting. Electric power is produced by the electric generator of a wind turbine that catches wind power through its wind rotor that is mainly driven by the lift force on its rotor blade. Airfoil characteristics such as airfoil shape, cord length, camber and airfoil twist are utilized to generate lift force that is perpendicular to the rotor axis. Although horizontal axis wind turbines have been widely used on wind farms, there is still room to further improve their efficiency and power generation. In this research, the power conversion efficiency or coefficient of a wind rotor is improved from airfoil twist. The airfoil twist angles of a rotor blade are selected based on maximizing the ratio between lift and drag forces. Three blade twist configurations are introduced for three different tip speed ratios. Four blades that have the three optimal and one reference twist configurations and their corresponding rotors are modeled and simulated. The simulation results show that the power conversion coefficients of the rotors with the optimal twist configurations have significant improvements on power conversion efficiency over that of the reference rotor.