SiC nanowires (SiCnws) were incorporated in supercritical-ethanol-dried graphene aerogel (GA-S) via chemical vapor infiltration (CVI) to fabricate a lightweight, thermostable, high-performance electromagnetic (EM) absorbing composite. The SiCnws improved the yield strength of GA-S from 0.15 MPa to 0.47 MPa in the linear elastic region. The oxidation temperature of GA-S contained in situ grown SiCnw exceeded 660 degrees C in air. The double-scale surface roughness increases the water contact angle from 53 degrees of GA-S to 134 degrees of SiCnw/GA-S. The SiCnw/GA-S composite showed a minimum EM wave reflection loss (RL) value of -54.8 dB at 5.3 GHz with thickness of 3.63 mm. The SiCnw/GA-S sample demonstrated a wide effective absorbing bandwidth of 6.5 GHz from 9.3 to 15.8 GHz at thickness of 2.0 mm. In addition, the SiCnw/GA-S sample could achieve effective absorption covering the entire X-band in a wide thickness range of 2.2-2.7 mm. Three-dimensional networks and residual oxygen functional groups of GA-S, the high-density stacking faults, and the abundant interfaces between SiCnws and graphene sheets played important roles in enhancing the EM dissipation of SiCnw/GA-S composites. The SiCnw/GA-S composites are promising EM-wave-absorbing materials in extreme environment. (C) 2018 Elsevier B.V. All rights reserved.