A portable terahertz security inspection apparatus, comprising: a carrying body; a terahertz emitting device arranged on the carrying body, wherein the terahertz emitting device comprises a terahertz signal source and an emitting unit connected to the terahertz signal source and configured to emit a terahertz wave; a terahertz detector arranged on the carrying body and configured to receive the terahertz wave reflected from an inspected object, wherein the terahertz detector comprises a terahertz lens, a terahertz detection chip and an adjustment flange configured to adjust a focal length of the terahertz lens; a data acquisition and processing system arranged in the carrying body and connected to the terahertz detector, wherein the data acquisition and processing system is configured to receive a scan data for the inspected object from the terahertz detector and generate a terahertz image; and a display device connected to the data acquisition and processing system and configured to receive and display the terahertz image from the data acquisition and processing system; characterised by: a distance sensor arranged on the carrying body and connected to the data acquisition and processing system, wherein the distance sensor is configured to sense a distance between the inspected object and the portable terahertz security inspection apparatus; and wherein a pre-processed signal acquired by the terahertz detection chip is compensated and optimized by the data acquisition and processing system based on the distance, and the terahertz lens is automatically calibrated by the adjustment flange based on the distance measured by the distance sensor. a carrying body; a terahertz emitting device arranged on the carrying body, wherein the terahertz emitting device comprises a terahertz signal source and an emitting unit connected to the terahertz signal source and configured to emit a terahertz wave; a terahertz detector arranged on the carrying body and configured to receive the terahertz wave reflected from an inspected object, wherein the terahertz detector comprises a terahertz lens, a terahertz detection chip and an adjustment flange configured to adjust a focal length of the terahertz lens; a data acquisition and processing system arranged in the carrying body and connected to the terahertz detector, wherein the data acquisition and processing system is configured to receive a scan data for the inspected object from the terahertz detector and generate a terahertz image; and a display device connected to the data acquisition and processing system and configured to receive and display the terahertz image from the data acquisition and processing system; characterised by: a distance sensor arranged on the carrying body and connected to the data acquisition and processing system, wherein the distance sensor is configured to sense a distance between the inspected object and the portable terahertz security inspection apparatus; and wherein a pre-processed signal acquired by the terahertz detection chip is compensated and optimized by the data acquisition and processing system based on the distance, and the terahertz lens is automatically calibrated by the adjustment flange based on the distance measured by the distance sensor. a distance sensor arranged on the carrying body and connected to the data acquisition and processing system, wherein the distance sensor is configured to sense a distance between the inspected object and the portable terahertz security inspection apparatus; and wherein a pre-processed signal acquired by the terahertz detection chip is compensated and optimized by the data acquisition and processing system based on the distance, and the terahertz lens is automatically calibrated by the adjustment flange based on the distance measured by the distance sensor.