The invention discloses a terahertz active security check instrument comprising a terahertz radiation source which is used for generating terahertz and is an electric vacuum device and of which the output end is connected with an antenna used for emitting terahertz to an object to be detected, an optical system which is used for receiving and transmitting the terahertz reflected by the object to be detected, a terahertz detector which is used for receiving the terahertz transmitted by the optical system and is arranged at the terahertz output end of the optical system, and an image processing system which is used for outputting a security check image and is connected with the terahertz detector. According to the invention, an electric vacuum device is used as the emission source of the terahertz active security check instrument, the security check effect identical to that of a camera is achieved, and the security check rate up to 24 frames per second is achieved. Moreover, whether an object to be detected (such as a human body) carries a gun, controlled knife or ceramic knife as well as the position of the dangerous article on the human body can be detected.