The propagation behaviour of terahertz (THz) pulses at an edge is characterized. The phenomenon that the amplitude oscillates periodically in the frequency spectrum is similar to Young's interference, if the absorption effect is neglected. The oscillation cycle is shorter for a thicker sample. THz pulses at an edge are analyzed by the broadband Huygens-Fresnel diffraction integral. The experimental results are in agreement with the simulation results approximately. The simulation errors are also analyzed.