Abstract: Thermal/mechanical properties of the fuels are dominantly affected by the fission pores produced from fuel particles during irradiation. In this paper, the effect of U₃Si₂ fuel particle on U₃Si₂-Al dispersed fuel were studied using the optical microscope（OM）, scanning electron microscopy（SEM） and energy dispersive spectrometer（EDS）. The microstructure of U₃Si₂ was observed. Additionally, the morphology, size and distribution of pores of U₃Si₂ were analyzed statistically. The results show that when the fission density increases from 2.34×10²⁷f/m~3 to 3.74×10²⁷f/m~3, the gas morphology in the U₃Si₂ fuel particles is globular and without great change. However, the average pore size and porosity caused by the fission pores increase with the fission density, which go through two stages: when the fission density of the fuel particles increases from 2.34×10²⁷f/m~3 to 3.19×10²⁷f/m~3, the average pore size and porosity are with steady-state growth; when the fission density of the fuel particles increases from 3.19×10²⁷ 3.74×10²⁷f/m~3, the average pore size and porosity increase rapidly.