A new kind of sealing composite material reinforced mainly with aramid and pre-oxidized fibers were developed by molding preparation method. The effect of different surface treatment methods of the fibers on the heat resistance of the composite material was studied. The optimum prescription of the sealing composite material was obtained by regression design method. The relationship between the transverse tensile strength of the material after ageing at elevated temperatures and its main ingredients was investigated. The performances of the developed sealing composite material were tested, and the results indicate that the main performances of the material coincide with the requirements prescribed in Chinese national standard and some performances are even better than that of the products of some famous corporations.