Abstract: Based on the three-dimensional multi-physical field governing equation of the composites, the thermal and mechanical responses, such as temperature field, displacement field, pore pressure and resin residual ratio of the silica/phenolic composites during volume ablation process were studied by finite element method. The calculation results reveal that the predicted temperature field and displacement field are in good agreement with the experimental results. It is found that the peak value of pore pressure in the solid material appears at the initial thermal decomposition region, while the peak value of elastic stress is in the original material near thermal decomposition layer.