The invention relates to a model selection and optimization method for a fan blade in a wind power plant. A simple and convenient multi-wind-direction wake flow calculation method is provided; the relative position relationship of fans can be obtained through conversion of rectangular coordinates and polar coordinates, so that the wake flow can be calculated; the wind speeds of various fan unit are calculated according to a wake flow effect formula; the generated energy at the corresponding wind speed is obtained according to an active output model of the fans; the practical power output of the various fan units is obtained through an interpolation method; the target is the lowest full-life-cycle KWH cost of the wind power plant; on the premise of sufficiently considering the wake flow effect among the wind speed distribution, the wind direction distribution and the units of the wind power plant, optimal selection of the blade lengths of the various fans in the wind power plant is carried out; and the optimization problem is solved through a genetic algorithm. On the premise that the installation capacity of the wind power plant is not changed, the benefit of the wind power plant is increased; the KWH cost is reduced; and guidance is provided for model selection of a wind power unit in the wind power plant planning stage.