In order to solve the problem of automatic evaluation of photovoltaic panel surface cleaning effect, an evaluation method of photovoltaic panel surface cleanliness based on image morphological filtering is proposed. Through the real-time detection and evaluation of the cleaning effect of photovoltaic panels, the collected surface images of photovoltaic panels are verified by experiments. Considering the adverse effects of grid lines and possible occlusions on the surface of photovoltaic panels in the process of dust quantification, a histogram based binary segmentation method and a mask making method based on two directions of closed operation are used to eliminate the grid lines and possible occlusions on the surface of photovoltaic panels. The experimental results show that the proposed method can effectively remove the grid lines and occlusion areas in the image of photovoltaic panels, effectively detect stubborn stains or occlusions, and realize the real-time evaluation of the surface cleanliness of photovoltaic panels.