Abstract: In order to solve the problem that the partial shading region segmentation of photovoltaic（PV）modules disturbed by the environment in the real scene,an image processing based partial shading region segmentation of PV systems is proposed in this paper.According to the characteristics of PV modules,firstly the module frame is extracted by the improved threshold segmentation method,secondly the module frame lines are detected by Hough transform,then the minimum convex hull surrounding the endpoints of the frame lines is calculated as the ROI. The partial shading region in the ROI is extracted by the improved threshold segmentation method. The effectiveness of the proposed method is verified by simulated images and real scene images. The experimental results show that the proposed method can accurately segment the partial shading region on the PV module and maintain the details of the shading region.Compared with multiple threshold segmentation method and Canny edge detection based segmentation method,this method has smaller misclassification error and higher class pixel accuracy.