Abstract: Low-density SiO₂ aerogel as the medium for thermal wave increase and high-efficiency laser-X ray (K shell) conversion attracts more and more attention. Two-step (acid-base) sol-gel process and CO₂ supercritical fluid drying technique were used to prepare SiO₂ aerogel with the density of about 10 mg/cm³ in gold hohlraum with the internal diameter of 800 μm and the length of 1 200 μm by in-situ forming technique. X-ray phase contrast imaging, optical microscope, and SEM were used to characterize the microstructure of aerogel in gold hohlraum and interfacial structure between aerogel and gold hohlraum. The results show that aerogel/gold hohlraum interface is closely combined and the density of aerogel near interface is lower than that of the interior. Furthermore, effects of interface characteristic on in-situ forming of aerogel, and the formation mechanism of structure differences about in-situ forming aerogel were discussed.