A technology for detecting laser-induced damage on optics, using line-scan imaging and dark-field image principle, is proposed. According to the phase differential theory, this technology only responds to laser-induced damages which cause the phase change, and thus the detected images have high contrast. In order to understand the features of the technology, the principle of the technology is analyzed, and the characteristics of the detection technology are verified by experiment. Experimental studies reveal that the technology can acquire high contrast and high-resolution laser-induced damage image, and that it has the potential to quickly detect the laser-induced damage of large aperture optical components.