Semiconductor quantum dots（QDs）are inorganic nanocrystals consisted of a cadmium selenide (CdSe) core which was wrapped in an outer shell of zinc sulfide (ZnS). In comparison with common organic dyes, this class of fluorescent labels is 20 times as bright, 100 times as stable against photobleaching. The emission wavelength of QDs was controlled by the size of the core and each single-color of QDs has narrow symmetrical emission peak. These advantages of the optical properties make them broad applications in medical diagnosis，high-speed screening drugs and high-throughput analysis of genes and proteins. Based on the stability and biocompatibility of the QDs, it is possible to make movies of long-term interaction of biological molecules in a living cell by tagging each biomolecule with different color of QDs.