Abstract: This paper introduces the digital light processing ( DLP) technology as the main principle of 3D printing technology and discusses issues on optical system in detail. This existing 3D printing technology, the principle of stereolithography technology and DLP technology were introduced. Introduced with DLP technology as the core of 3D printing technology, including the basic structure of the system, and how DLP technology used in rapid prototyping were explained. And the digital micro-mirror device ( DMD) composition and the driving principle, the typical structure of an optical system used in DLP technology, as well as their effects on 3D printing technology were interpreted. Then, the 3D printing applications, and the problem of DLP technology such as the suitable DLP optical system wavelength, the projection format uniformity, and molding accuracy were discussed. Finally, the advantages and disadvantages and disadvantages of DLP technology in the field of 3D printing were summanized.