Abstract: A mathematical model according to st ructural feature of Si₃N₄ particle reinforcement and process characteristic of isothermal chemical vapor infilt ration ( ICVI) was proposed to numerically simulate the densification behaviors of Si₃N₄ particle reinforced Si₃N₄ composites. The ball-like pore model is developed to depict the st ructure ofSi₃N₄ 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 Si₃N_4P / Si₃N₄ composites.