The scattering of defects on the surface of the mirror directly affects the performance and accuracy of the optical testing system. The scattering of the surface defect of the mirror can be detected by the laser scattering microscope. In order to ensure the detection efficiency and precision of the whole system, the microlens lens, the size of the spot and the power spectrum response of CCD are designed in the design of the hardware system. The software of microscope imaging test system can use step motor to scan the mirror surface, control the image acquisition card to collect the image and save the image. It focuses on how to accurately and accurately collect the sub aperture images, and lay a foundation for subsequent image mosaic. By analyzing the accuracy of the whole test system, it is able to distinguish 5~10 μm defects by ×20 magnification.