The structure evolution of multi-walled carbon nanotubes (MWCNTs) in low-carbon Al2O3-C refractories with silicon additive was investigated. The structure evolution of MWCNTs at different coked temperatures was analyzed by X-ray diffraction, scanning electron microscopy and transmission electron microscopy, respectively. The results show that the diameter of MWCNTs decreases at 800℃ due to the oxidization of partial walls of MWCNTs. When the temperature is increased to 1000 ℃, SiC coating is synthesized on the surface defects, and even a part of MWCNTs is transformed into SiC nano-whiskers. The transformation process is accelerated and the synthesis of considerable SiC whiskers is also stimulated when coked at 1200 and 1400 ℃. The morphology of SiC whiskers appears curved when MWCNTs convert. There are numerous straight SiC whiskers formed at high temperatures due to the vapor reaction of SiO and CO.