The work aims to improve the ablation resistance of C/SiC engine nozzle. The turbulence model of engine nozzle was established based on mass, energy conservation and physical property equation. The linear ablation rate of nozzle substrate and each coating was calculated by numerical simulation method, and the accuracy of the model was verified. Multi-component composite coating system was established by comparing the ablation resistance of different types of coatings and the coating matching. The ablation behavior and ablation mechanism of the system were analyzed to calculate the linear ablation rate of HfO2-ZrC-SiC-C/SiC Quaternary system at different temperature. The oxidation ablation performance of Hf and Zr coatings was excellent, and the maximum linear ablation rate was between 0.3~1.2 μm/s. HfO2 had good ablation performance and stability. The ablation rate at the throat and diffusion section of HfO2-ZrC-SiC-C/SiC system was lower compared with other systems. At 7MPa, the linear ablation rate was calculated at 1700 K, 2100 K, 2500 K and 2900 K, and the maximum linear ablation rate region was migrated. The ablation rate of each temperature gradient respectively increased by 174%, 20.22%, 18.04%. HfO2 can effectively reduce the ablation rate of the convergent section of the nozzle and is appropriate for being used as the outermost layer in the composite system. In addition, the increase of temperature significantly aggravates the ablation of chemical reaction and mechanical denudation, and mechanical denudation becomes the main ablation mechanism at high temperatures.