Brittle materials are usually used as raw materials for optical elements. Subsurface damage (SSD) is easily generated during the processing of brittle materials. SSD causes serious hazard to the manufacturing and application stage of brittle materials. In terms of manufacturing, SSD affects the selection and connection of processes, which is easy to cause problems such as excessive processing and lack of processing, and resulting in low processing efficiency. In terms of application, SSD affects key technical indicators such as imaging quality, stability, and service life of optical components. Comprehensive characterization and accurate measurement of SSD in optical components is critical for efficient, and high-quality removal of SSD. In this paper, the formation mechanism of SSD corresponding to different processing methods and the characterization methods of SSD are introduced firstly. Then the destructive and non-destructive SSD measurement methods are summarized. The principles, applicable materials, applicable processing stages, advantages and disadvantages of different measurement methods are introduced, respectively. The SSD prediction methods based on surface roughness and processing parameters are presented. Finally, the development trend of SSD measurement technology is prospected.