A digitalized ultra sensitive fluorescence microscope has been developed, in which an intensifier CCD is used as high sensitive image detector with luminance gain of 41,000. It can detect ultra weak fluorescence image and decrease the concentration of fluorescence label and emitting light intensity in order to keep natural situation of the detected cell. This digitalized microscope can be used not only to obtain the fluorescence image, but also get the light luminance at every point of the image and the average light luminance of the whole image quantitatively. With this instrument, we have obtained: 1) The image of hypocrellin-A distribution in HeLa cell, it shows the HA is mainly absorbed by cell membrance; 2) The image of HeLa cell be oxidated by strong light after adding HA; 3) Images of HeLa cel being protected by three antioxidant reagent Vit. E, sodium ferulate (SF) and butylated hydroxytoluene (BHT), from which it has been shown that anti-oxidated effect of Vit E is the best; 4) The curve of absorbed quantity of HA in a HeLa cell with time versus culture time; 5) The curve of absorbed quantity of HA in Hela cell versus concentration of HA solution.