A ceramifiable and flame‐retardant silicone sealant was prepared by adding aluminum oxide and crosslinkers, coupling agents, and catalysts into hydroxy silicone oil. After ablation at 1000°C for half an hour, a ceramic shell with a certain strength was obtained. The impacts of the viscosity of the hydroxy silicone oil and the content of aluminum oxide on the flame‐retardant properties, mechanical properties, surface properties, and ceramification compressive strength of the composite material were studied. The composite with the highest aluminum oxide content could reach an FV‐1 vertical flame rating and a limiting oxygen index of 29.6%, and the ceramification compressive strength could reach 0.15 MPa. This ceramifiable has a wide range of application prospects in industries such as building decoration and wire and cable.