Most of the existing infrared-imaging-based methods for circuit fault detection usually need the corresponding standard reference infrared images for comparison,which restricts their practical application. A novel operating temperature and fault detection algorithm for circuit-board-mounted devices without standard reference infrared images is proposed. The region growing and eliminating technique is employed to extract heating areas. Then,the surface temperatures of heating devices are calculated by using least squares and quartic polynomial fitting methods. According to ambient temperature and device package,the temperatures of internal PN junctions of heating devices can be calculated to judge the device fault. Experiments are conducted under Ubuntu16.04 and OpenCV3.0,and experimental results verify the validity of this algorithm.