The paper introduces the steady model of wind turbines with an asynchronous generator. Based on the conventional RX model

the difference between mechanical power and electric power for a wind turbine

and the slip of an asynchronous generator are introduced into the correction function of Newton iteration method to form an expanded correction function. The method avoids the two iteration loops needed for the conventional RX method and retains the quadratic convergence speed of Newton iteration method. An acceleration factor is also proposed in the method to enhance the convergence speed. An application to the power flow calculation for the Changma Wind Farm in Gansu Province proved the feasibility of the proposed method.