With the aim to design a particular material for low and high frequency cooperative electromagnetic absorption at high temperature, a multiscale design is proposed by combining the microstructure and meta-structure in one material. The SiCf/Si3N4 composite is prepared via the chemical vapor infiltration technique with SiCf as the EM wave absorbing phase and Si3N4 as the wave-transparent ceramic matrix. The crossing grooved meta-structure is designed and fabricated to further improve its absorbing properties and to guarantee its absorbing capacity stability at high temperature. A minimum reflection loss of -15.3 dB and -14.8 dB can be reached at 8 and 18 GHz with a total thickness of 5 mm. The temperature-dependent reflection loss of the designed meta-structure keeps relative reliable high temperature absorbing performances from room temperature to 500 degrees C. This effective enhanced EM wave absorbing property is believed to be a consequence of multiscale effect induced by combining the traditional EM absorbing materials with metamaterial structure.