A Terahertz radar for the measurement of the spacecraft reentry capsule is designed to solve the missing problem of the radar target caused by the plasma during the reentering process of the spacecraft reentry capsule, by using the characteristics that THz waves can penetrate the plasma. Due to the low power of THz transmitter, and the high loss of THz waves in the atmosphere, the airborne THz radar is adopted to measure the spacecraft reentry capsule. The analysis results show that the airborne THz radar is easy to be realized in engineering applications.