A new optical element was proposed, which could generate a diffraction-free beam with a certain distance from the element. The cross section of an ordinary axial pyramid was an isosceles triangle and the element was designed by defining a parabola on the two waists. The 3D printing technology was used to fabricate optical elements with different structures. The results of simulation calculation using angular spectrum theory and the experiment conducted at 0.1 THz frequency clearly show that there is a certain distance between the generated diffraction-free beam and the element. The beam behavior of the element was analyzed according to the spatial frequency spectrum. The results show that the element generates a new type of diffraction-free beam, and according to the space-frequency shape of the element, the diffraction-free beam generated by the element is named comb-like space-frequency diffraction-free beam.