Abstract: A terahertz (THz) quasi-near-field real-time imaging system was presented, with which three industrial flat cables with minute structures were nondestructively tested. In the obtained image at the peak of signal, data from metal, defect, and cladding material were extracted and Fourier transformed, and then comparisons and analyses had been performed in the time domain, frequency domain and phase domain. Furthermore, images for amplitude and phase were obtained by processing the original images, and it showed that the phase images reflect the defects more obviously than others. Testing results showed that THz quasi-near-field real-time imaging could be widely applied in quality monitoring and inspection of materials with minute structures.