The invention belongs to the crossing field of electromagnetic shielding materials and refractory materials, and mainly relates to an electromagnetic shielding composite and a preparation method thereof. The composite comprises SiC fiber reinforcement, a resin carbon interface layer and a Si-O-C matrix, and the resin carbon interface layer is located between the SiC fiber reinforcement and the Si-C-C matrix. The prepared composite has an electromagnetic shielding function and can be used in a high-temperature oxidizing atmosphere at the temperature of 900 DEG C. The shielding effectiveness of electromagnetic waves of the prepared composition reaches 25 dB or above within the frequency range of 8.2 GHz to 12.4 GHz, the shielding effectiveness can be optimized and main absorption and main reflection can be converted by changing the thickness of the pyrolytic carbon interface layer, and the shielding effectiveness of the composite can be still kept at 16 dB or above after being oxidized for 4 h in air at the temperature of 900 DEG C.