Abstract: The silicon aerogel substrate was prepared by a two-step base/acid catalyzed sol-gel process using tetraethoxysilane(TEOS) as silicon source and by freeze drying. By adding different content of triethylamine hydrochloride(TEAHCl) to the substrate during the aging process, composite aerogels with broadband absorption in mid-and far-infrared windows was prepared. The structure and property of composity aerogels were characterized by X-ray diffraction(XRD), scanning electron microscopy(SEM), N2 physisorption at 77 K and Fourier-transform infrared spectroscopy(FT-IR). Results show that the triethylamine hydrochloride is crystallized adhering to the whole three-dimensional network of silicon aerogel. The silicon aerogel substrate has the specific surface area about 524.5 m2/g, total pore volume about 1.2 cm3/g and average pore diameter about 9.2 nm. The composite aerogels have the specific surface area about 37.93-138.7 m2/g, total pore volume about 0.08-0.28 cm3/g and average pore diameter about 7.1-8.8 nm. The apparent density of silicon aerogel substrate and composite aerogels are 0.25 g/cm3 and 0.35-0.51 g/cm3 respectively. The composite aerogels have the characteristic of broadband absorption in mid-and far-infrared windows. The relative absorption intensity in mid-infrared window increased in proportion with the increase of TEAHCl.