A set of microscopic transmission and reflection spectrum system was set up, which can be use to measure the transmittance of individual cell precisely. With this system, we measured the transmittance of alga cell and leukemic leukocytes with and without medication. The results show that: 1) the absorbing peak of alga cell is consistent with that of chloroplast, from which it can be seen that chloroplast is the major organelle for absorbing energy of light;2) there is great difference between two kinds of leukocytes in their transmittance, which suggests that the cell was changed with medication. This is instructive on improvement of photosynthesis efficiency, cell identification and drug screening.