Abstract: A THz imaging system based on the theory of compressed sensing was described, the theory break through the limit of Nyquist sampling law, it can reconstruct the original image by only a small number of measurements, so that it can shorten the imaging time and improve the utilization of memory resources to a large extend. Through the analysis of the theory, the three important factor of the theory are the transform matrix, the measurement matrix, and the reconstruction algorithm. A series of simulation was done to contrast different transform matrixes, different measurement matrixes and different reconstruction algorithms respectively, and according to contrast results, the most suitable transform matrix, measurement matrix and reconstruction algorithm for the image object were decided. Finally, the imaging system was set up by off-axis throw lens instead of polyethylene lens, and preliminary experimental results were made by this experiment system.