This work introduces a thermal fault diagnosis method that integrates superpixel segmentation and low-rank representation for diagnosis. The proposed method comprises two main steps. First, an input infrared image is transformed using a principal component analysis (PCA) algorithm, and a superpixel segmentation method is employed for the first principal component (PC). The first PC is divided into non-overlapping homogeneous superpixels. Then, the thermal fault region is detected by employing low-rank representation in a superpixel-by-superpixel manner. Experimental results show that the proposed diagnosis method has a better detection performance than that of current state-of-the-art detectors.