Abstract: The key technology of fluorescence lifetime imaging microscopy is introduced. Time-correlated single photon counting in time-domain method is adopted to record fluorescence lifetime. The counting efficiency and the amount of information in the data can be increased by recording the fluorescence in several wavelength channels simultaneously. Multi-wavelength imaging is used to separate different chromophores in stead-state images. Thus the image is build up with four dimension. On the other hand, multi-photon exciting technology is used in the system. Two or more photons emitted by long-wave light source can excite a short-wave one. Several photons must reach the excited point simultaneously to produce enough energy to excite fluorescence. The long wavelength emitting light in multi-photon