Abstract: The black spot defects of liquid crystal were studied and analyzed by means of super-depth-of-field microscopy, scanning electron microscopy and energy disperse spectroscopy. The results show that the black spots are corrosion pits in the Al layer of the reflective film of the polarizer, with the residue of I element. The higher the content of I element, the more serious the corrosion is. Through double 85 aging test, the defects can be quickly reproduced. The analysis shows that I₂ adsorbed by PVA film sublimates at high temperature, penetrates through TAV film and contacts with the Al layer of the reflective film. Under the catalysis of H₂O, redox reaction occurs to generate AlI₃, leading to the corrosion of the Al layer of the reflective film. Increasing the concentration of I₂ solution and dyeing time as well as increasing the tensile ratio of PVA film can enhance the adsorption capacity of I element on PVA film, which can effectively improve the quality and reliability of liquid crystal.