In this paper，silica-phenolic resin and the asbestos-phenolic resin (5-Ⅱ^#) reinforced plastics are researched experimentally. Some pyrolytic parameters of these ablatíve composite materials are determined. The approximate formulae of the density and the pyrolytic rate function are delermined by the least square method. The data and these formulae used in this paper can be used as a basis for the calculation of the ablative materials.