Phenolic impregnated ceramic ablator (PICA-X) were prepared by impregnation of novolac phenolic resin solutions into mullite fiber mat, followed by so-gel reaction and ambient drying. The density of the PICA-X could be adjusted in a range of 0.45 to 0.50 g/cm³ by using different concentrations of novolac phenolic resin solutions. The microstructure, mechanical property, thermal insulation property and thermal stability of PICA-X before and after carbonization were systematically investigated. PICA-X, which are composed of phenolic aerogel reinforced by mullite fiber, exhibit excellent mechanical strength of 26.7 to 34.0 MPa and low thermal conductivity of 36 to 40 mW/(m·K). After carbonization at 1 000℃, the flexural strength and thermal conductivity of the resulting C-PICA-X are 13.9 to 14.5 MPa and 41 to 45 mW/(m·K), respectively. In addition, PICA-X exhibits good oxidation resistance before and after carbonization.