The work aims to improve ablation resistance of C/C composites by preparing SiC coating on C/C composites. A pure Si coating was prepared on C/C composites by adopting vacuum plasma spraying (VPS) technology and then SiC coating was generated in situ by performing high-heat treatment in inert atmosphere as pure Si coating reacted with C element at high temperature. The stagnation point ablation property of coating was evaluated on arc heater at different temperature. Microstructure and phase composition of the coating before and after ablation were characterized with optical microscopy, scanning electron microscopy, energy dispersive spectroscopy and X-ray diffractometer. A compact SiC coating free from obvious cracks was prepared on C/C composites. Deep permeation zone was present beneath the coating and the depth exceeded coating thickness. As-prepared SiC coating was complete and of good stagnation point ablation property as the coating has been ablated at 1400 ℃ for 50 s. However, local coating peeled off at 1600 ℃ and 1650 ℃ after 50 s ablation to make the C/C composites ablated. The SiO2 glassy scale covering the surface of C/C composites is formed on SiC coating at high temperature, which can protect the C/C substrates. As the ablation temperature rises, provided with erosion of hyper-sonic flow, mismatched thermal expansion and active SiC oxidation, the temperature increasingly peels off along edges of ablated surface and cannot protect C/C substrate any more, so that ablation resistance of the coating decreases.