Nondestructive testing (NDT) is becoming more and more important nowadays, visual nondestructive testing (VNDT) such as imaging instead of traditional testing methods becomes popular and highly demanded, which makes it possible to see the internal state of objects visually. The magneto-optic (MO) microscope technology for nondestructive testing is detailedly introduced in this paper, include two different MO imaging system to test the buried subsurface defects in metallic and magnetic specimens.