The principles ofTwo.Dimensional Spectrograph (TDS) fbr the Space Solar Telescope (SST) arc described in this article. The TDS will be the main focus plane instrument of thc payload of SSL It is a kind of birefringent filtcr with polaroids replaced by polarizing beam spliLter. It permits observations of solar. vector magnetic field or lincof-sight velocity fields in any Fraunhofcr line in the wavelength region from 3900 in 6600 angstrom with half width horn 0.03 to 0.12 angstrom. Lt can be turned across the spectral line to obtain linc profiles ofiwo-dirnensional field of view in one channel and also van be turned on one spectral line to obtain partofthe line profiles of two-dimensional field of view with 8 channels. This article also describes the analysis of mechanicul and thermal control of the TDS. In the finale, a new polarimeter of this system is introduced.