CVD-Si3N4/CVD-SiC/pack-SiC/pyro-carbon/(3-D C/C composite) multilayer coating was performed to improve the oxdiation resistance and erosion resistance properteis of the 3-D carbon/carbon composite, and the plasma test was performed to measure the oxidation resistance and erosion resistance properties. The thicknesses of each film layer were about 10${mu}{ extrm}{m}$ for pack-SiC, 5${mu}{ extrm}{m}$ for CVD-SiC and 40${mu}{ extrm}{m}$ for CVD-Si3N4. When the multilayer coated specimen was exposed to the plasma flame with temperature of 500$0^{circ}C$ for 20 seconds, it showed the weight loss five times less than that of the only pyro-carbon coated specimen.