Abstract: It is great important that the mechanical, thermal properties and structure of extreme density carbon aerogel will directly affect its application scope, since carbon aerogel with adjustable structure and density are designed as a conventional target in ICF research and X laser experiment. Low-density (36 mg/cm³) resorcinol-formaldehyde carbon aerogel was fabricated by improving the traditional synthesis technique and adjusting the parameters of reactants. Field emission scanning electron microscope, X-ray diffractometer, BET and simultaneous thermal analyzer were used to observe the microstructure of low-density carbon aerogel, while dynamic mechanical analyzer, electronic tensile tester and thermal constant analyzer were used to characterize its properties. The research shows that the low-density carbon aerogel processes the unique pearl necklace-like nano network with homogametic nanoparticle of about 70 nm. Its specific surface area is 1 217 m²/g before activation. It is a perfect elastic material with stable mechanical properties. Its Young’s modulus is only 0.375 MPa from -120 ℃ to 200 ℃, much less than that of the regular density carbon aerogel. Its thermal conductivity is as low as 0.05 W/(m•K) at ambient conditions, which has been greatly improved from the conventional carbon aerogels.