Infrared broadband antireflection components were successfully fabricated using a microstructure approach combined with a coating method. First, the influence of period, filling factor, height, and film thickness on the required band transmittance was simulated using FDTD Solutions software. As such, the microstructure and film parameters corresponding to good antireflection were obtained. Then, according to these parameters, a parabolic cone microstructure was prepared onto the surface of a sapphire through laser interference lithography combined with reactive ion etching technology. Finally, a SiO2 film layer was coated onto the surface of the microstructure. Test results show that the average transmittance of samples with single-sided microstructure and composite structure at 1.5--4 μm were 92.3% and 98.7%, respectively. Therefore, the transmittance increased by 11.0% compared with double-sided polished sapphire samples. Infrared broadband antireflection of the sapphire was obtained. Finally, a high-and-low temperature cycle and humidity experiment was conducted on sapphire element with composite structure. This experiment shows that the change in transmittance was not obvious and without obvious water absorption, indicating that the component has environmental durability.