Technology of stimulated emission depletion (STED) fluorescence microscopy utilizes the nonlinear relationship between the fluorescence saturation and the excited state stimulated depletion with nano-scale resolution. It implements the 3D imaging and breaks the diffraction barrier of the far-field light microscopy by restricting depletion zone at a sub-diffraction spot. Based on the physical process of STED, inhibition mechanism of stimulated emission and working conditions of depletion are reasonedly elaborated. The resolution of STED system and components are described. The STED microscopy has developed with many extendible technologies, such as two-beam, two-photon, dual-color, 4Pi and triplet-state relaxation. Finally, the latest laser technology related to STED, and the application prospect of STED microcopy are introduced.