Silicon carbide (SiC) as a kind of high temperature absorbing materials has great application potential, but its application range is limited due to high preparation cost. Herein, the SiC absorbing materials by in-situ reaction of pyrolytic carbon and silicon powder were prepared in vacuum at 1800^oC, 2000^oC and 2200^oC respectively, aiming to clarifying the relevant reaction mechanism so that to search the way for saving preparation cost. The microstructure, phase composition and electromagnetic properties of the three kinds of SiC materials were assessed. The results show that during the in-situ reaction of SiC preparation, the β-phase SiC with 3C crystallographic structure is formed at 1800^oC, while at 2000^oC the β-phase SiC begins to transform into α-phase SiC with 6H crystallographic structure via evaporation and condensation processes. With the increase of the reaction temperature, the degree of phase trasformation reaction was gradually intensified. Spontaneously, the proportion of α phase SiC also increases gradually, and the dielectric loss ability of the corresponding SiC materials to electromagnetic waves is gradually weakened, the impedance matching performance is gradually improved. In brief, the prepared SiC material presents appropriate comprehensive performance of dielectric loss and impedance matching when the preparation temperature is set above ≥ 2000^oC, suitable for use as a wave absorbing material. The results show that it is feasible to prepare SiC absorbing materials with low preparation cost by in-situ reaction method.