Coating technology is a main method to improve ablation resistance of C/C composites at high temperature. Zr-Mo-Si-C composite coating was prepared on graphite substrate by low pressure plasma spray. The ablation resistance of the coating was tested by oxyacetylene flame. The phase composition and microstructure of the coating were studied by XRD, EDS and SEM, respectively and the ablation mechanism of the composite coating was also analyzed. The coating was in good condition after ablation at 1800 ℃ for 60 s, 180 s and 300 s and the linear ablation was respectively 1.2×10?3 mm/s, 0.4×10?3 mm/s and 0.3×10?3 mm/s. For 300 s’ ablation, there were three areas on the cross section of the coating, respectively ablative area, barrier layer and non-ablative area. The ablation resistance of ZrC coating can be improved by adding MoSi2 as the second phase. The coating shows three areas during ablation, ablative area and barrier layer can effectively inhibit the ablation and non-ablative area forms sintering densification to further improve the oxidation and ablation resistance of coating.