To prove up the property of numerous crystals found in the cells of tea foliage suffering fluorescent green spot disease, the methods of scanning electronic microscope, electron probe, X ray powder diffraction and chemical analysis were applied to observe the shape of crystals, identified the chemical molecular formula and analyzed the content and also its correlation with the degree of fluorescent green spot disease. Results showed the crystals belonged to the type of calcium oxalate, its molecular formula was CaC₂O₄·H₂O; But calcium oxalate was only covered on the surface layer of crystals, in which contained other substances. The morphology of crystals were four types, i.e. druse, prismatic, laminose and sand．The content of calcium oxalate increased in accordance with degree of disease. On the basis of statistical analysis, the effect of disease degree on content of calcium oxalate was obviously.