Abstract: Carbon fiber reinforced carbon aerogel composites were prepared by impregnating the fiber preform, gel aging, supercritical drying and carbonization. Resorcinol (R)-furfural (F) alcohol sol was synthesized by isopropanol (I) as solvent, hexamethylenetetramine (H) as catalyst. The effects of sol proportion on densities, microstructures and mechanical properties of carbon fiber reinforced carbon aerogel insulation composites were investigated. The results show that the densities of carbon fiber reinforced carbon aerogel insulation composites decrease gradually, the pores diameter and the amount of large pores in matrix carbon aerogels and the interface formed with carbon fiber increase, the strength of carbon fiber reinforced carbon aerogel insulation composites decreases with the increases of amount of substance ratio for isopropanol and resorcinol. When isopropanol and resorcinol amount of substance ratio increases from 18 to 28, the compressive strength decreases from 2.498 MPa (strain 10%)to 0.716 MPa (strain 10%), tensile strenghth decreases from 2.019 MPa to 1.001 MPa, bending strength decreases from 3.984 MPa to 1.818 MPa. The densities of carbon fiber reinforced carbon aerogel insulation composites increases firstly and then decreases, the pores diameter and the the amount of large pores in matrix carbon aerogels and interface formed with carbon fiber decreases firstly and then increases, the strength of carbon fiber reinforced carbon aerogel insulation composites increases fistly and then decreases with the increase of amount of substance ratio for hexamethylenetetramine and resorcinol. The densities and the strength of carbon fiber reinforced carbon aerogel insulation composites are biggest when amount of substance ratio for hexamethylenetetramine and resorcinol is 0.008 5, the compressive strength is 1.066 MPa (strain 10%), the tensile strenghth is 1.256 MPa, bending strength is 3.556 MPa.