A hybrid antireflective structure (ARS) is proposed for enhancing the transmittance of terahertz (THz) waves. This hybrid ARS was made by attaching a polymer-based two-layer coating onto a moth-eye structure on a silicon (Si) substrate. The measured power reflectance of this hybrid ARS remained below 6% in the frequency range of 0.6-2.5 THz, corresponding to the simulated results. The total power reflectance from 0.1 to 2.5 THz was 20% that of the unprocessed Si surface. Besides exhibiting a broadband AR characteristic, this hybrid ARS inherited the cleanable flat surface from the coating structure, which also acts as a protective shield for the moth-eye structures. This high-transmittance, cleanable, flat antireflective surface can not only improve the performance of numerous THz components but also promote the applications of THz waves in daily life.