As Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) project is going to be completed in 2008/2009, and Five hundred meter Aperture Spherical Telescope (FAST) have been approved by Government in 2007, and the site survey, led by the National Astronomical Observatories of CAS, in west China, and in Antarctica, have been

carried through in recent years, the Chinese astronomical community started to think about the next large astronomical facility which should be proposed and started to be built in next 10 years. A 30m aperture sub-millimeter telescope (TSMT) with an active reflector is suggested in this paper. To extend the observation band to far infrared wave length in 0.2mm, the technology developed in large optical telescope like LAMOST for segmented primary mirror is applied in the segmented reflector of this sub-millimeter telescope, but with much lower requirement in accuracy comparing with the 30m extremely large optical telescope. In this presentation, the optical system design, technologies related to the segmented active reflector, telescope structure design and others are described.