A mathematical model according to st ructural feature of Si
3N
4 particle reinforcement and process characteristic of isothermal chemical vapor infilt ration ( ICVI) was proposed to numerically simulate the densification behaviors of Si
3N
4 particle reinforced Si
3N
4 composites. The ball-like pore model is developed to depict the st ructure ofSi
3N
4 particle reinforcement and the mass t ransfer equation of reagent s is used to characterize the concent ration profile in the preform. The corresponding experiment was done in order to testify the mathematical model . The calculated result s represent the same densification regularity as the experimental data does , and the curves of calculatedinfilt ration time and porosity are in agreement with the experimental ones , which indicates that the model developedhere is reasonable to characterize the ICVI process of Si
3N
4P / Si
3N
4 composites.