The invention relates to the field of heat-resisting protection between a moving rudder and a fuselage of a high-speed aircraft, in particular to a phthalonitrile composite heat-resisting protection plate and a manufacturing method thereof. The front segment of the heat-resisting protection plate is a semi-conical protrusion, and the rear segment of the heat-resisting protection plate is in a flat plate shape. The composite heat-resisting protection plate is composed of 2.5D braided fabric and phthalonitrile resin. The volume ratio of the 2.5D braided fabric to the phthalonitrile resin is 100:(54-150). The 2.5D braided fabric is one of 2.5D quartz fiber braided fabric, 2.5D carbon fiber braided fabric and 2.5D glass fiber braided fabric or mixed braided fabric of the 2.5D quartz fiber braided fabric, the 2.5D carbon fiber braided fabric and the 2.5D glass fiber braided fabric. A product prepared through a forming technology of the phthalonitrile composite heat-resisting protection plate is high in temperature resisting level, good in dimension stability, small in high temperature deformation, good in bearing performance and remarkable in weight reduction effect; the problem that the mass is too high in a traditional metal scheme is solved; the problems that in a phenolic resin based composite scheme, the temperature resisting level is insufficient, and dimension deformation is large at the high temperature are solved; and the phthalonitrile composite heat-resisting protection plate is suitable for preparation of high-dimension-precision high-temperature-resisting composite components.