In the inspection of a wind turbine in a drone, abnormal illumination may seriously affect the quality of the captured images. As a result, the blades of the wind turbine have abnormal brightness in the images, and small defects such as cracks on the blades cannot be found effectively, which affects the stable operation of the wind turbine. For this reason, this study proposes an illumination analysis method for the inspection of wind turbines. Before the inspection, the illumination situation is prejudged according to the planned trajectory and solar orientation. During the inspection, the illumination of the key parts is analyzed according to the segmentation results of the blades and tower barrel. In this process, we introduce a method of illumination analysis about the whole image based on weighted mean. In conclusion, the proposed method can predict the abnormal illumination in the whole inspection process and provide a basis for efficient and accurate inspections.