Terahertz band is the bridge connecting the electrical waves and light waves in electromagnetic spectrum. It is the latest developed band，and attracts much attention in remote sensing field. The advantages of Terahertz wave are analyzed in astronomical observation，metrological observation，target Radar Cross-Section(RCS) measurement，counter-stealth，and detecting radar applications，and their development trends are discussed and envisioned as well. The application of Terahertz radar in the scenes of ballistic target detection and space target alarm are discussed in detail. A good prospect is suggested for the application of Terahertz techniques in remote sensing fields.