With the increasing of the thermal field size of the straight-pull method, the C/C composite crucible-holder has been widely used to replace the graphite crucible-holder in the production of single crystal silicon. However, due to the high temperature and Si-riched environment, the crucible-holder made of carbon fibers are easy to disassimilated, the high frequency of replacement increases the production cost to the enterprise. In this paper, the phase at different stages of carbon fiber’s dissimilar coating were analyzed by XRD, and the morphology of the dissimilar coating was studied by SEM. It was found that carbon fiber turned into silicon carbide in the high temperature and Si-riched environment. By analyzing the flow field and temperature field of the monocrystalline silicon furnace, the formation process and mechanism of silicon carbide were revealed.The main reasons for the dissimilarity were analyzed. The results can provide theoretical support to prolong the service life of the crucible-holder.