Abstract: For the main light amplification of high-power solid laser devices, an on-line damage-detecting system is designed. With its invariable magnification specialty, a telescope is used to on-line detect any damage information on different optical components at equivalent precision and resolution. With the theory of depth of field, by accurately adjusting the size of exit aperture of the damage-detected system, we can obtain all kinds of damage on the same inclined optical component at the same time, and minimize the negative interaction between adjacent components. The brightness field imaging method is adopted to identify the damaged components, while the darkness field imaging method is applied to measure the distribution and sizes of damage spots on the same component. Experiments have pr