Developing coating materials, which are thermally insulating and high-strength support in extreme environments, is a hot spot for the thermal protection of aerospace. However, the lack of stable ceramic construction after prolonged thermal attack creates a risk of mechanical performance degradation. Herein, a silicon-based porous thermal protection composite was proposed by enveloping an innovative silicone resin on melamine frame. The thermostability of silicone resin was significantly improved by just 2 wt% addition of a multifunctional silane monomer, due to the incorporated diphenylamine and its derived quinonimine structure. Meanwhile, the uniform distribution of ammonium polyphosphate (APP) in the system effectively filled defects and cracks during pyrolysis. These facilitated the formation of an ordered porous polymer-derived ceramic framework under high temperature, thus significantly enhancing the material's mechanical strength (1200 °C, 3.39 MPa) and thermal insulation. Notably, even when subjected to prolonged high-temperature flame impact, the 3 mm-thick quinonimine-incorporated coating maintained its intact structure and preserved a backside temperature 77 °C lower than that of traditional silicone/melamine coating. This work provides a strategy for developing thermal protection composites that exhibit machinability, high strength, and superior thermal insulation performance in extreme environments.