Aiming at the problem that the existing small-scale cluster damage mitigation and detection technology is still imperfect, it focuses on the multi-modal in-situ detection method of sub surface defects, and systematically measures and analyzes the number and size of surface damage of damaged samples, the morphology of typical small-scale damage, light and heat absorption, fluorescent area and other indicators, and carries out magnetorheological repair research. The results show that the absorbent impurities inside the small-scale damage of fused silica are the main factors affecting the performance of the components. Before the magnetorheological ribbon contacts the bottom of the damage, the overall absorption and fluorescence distribution of the damage show an upward trend. The damage irradiation process of high repetition rate laser after magnetorheological repair is a process from slow to fast, from impurity to body, and gradually expanding outward from the edge. It can effectively repair the surface after magnetorheological repair, and can be used as the third process of combined repair process. The research results provide a reference for the construction of optical element detection and characterization system.