Abstract: Up to now, uranium dioxide (UO₂) is widely used in water-cooled nuclear reactors. It has the characteristics of high melting temperature, splendid irradiation stability, and excellent fission product capacity. However, UO₂ has a lower thermal conductivity, even its thermal conductivity decreases significantly with the increase of temperature and fuel consumption. Under severe accident conditions, the lower thermal conductivity can lead to the fuel’s center temperature so high that the core can melt, and then radionuclides will be released to the external environment. U₃Si₂ is considered as an accident resistant alternative fuel for UO₂ though it has higher thermal conductivity and uranium density than UO₂. However, U3Si2 fuel will produce a large number of point defects during irradiation. These defects tend to cluster and form voids or bubbles, causing fuel swelling through evolution. Continuous swelling of fuel will further affect the service life and the performance of fuel. Due to the service environment of U₃Si₂ fuel is extremely harsh and the experimental research cycle is long, the research cost is higher. It is very difficult to study the irradiation swelling of U₃Si₂ fuel through existing experimental methods, leading to lacking sufficient understanding of the evolution mechanism about its irradiation damage microstructure. Considering this situation, it is necessary to study the structure and performance of U3Si2 fuel by computer simulation. The first-principles, molecular dynamics and Monte Carlo methods have made significant contributions to the calculation of defect parameters, migration, and diffusion in U₃Si₂ fuel. Unfortunately, these methods ignore the spatial correlation between various microstructure features and evolution processes. Phase field simulation can consider the inhomogeneity of local microstructure at larger spatial and temporal scales, and more accurately simulate the evolution of voids under irradiation conditions. In this work, the phase-field method was used to simulate the void evolution of U3Si2 fuel in three-dimensional space, and the effect of fission density on the void evolution of U3Si2 was obtained. The results show that the size of void changes with the fission density in a power-law manner and satisfies the following equation 〈R〉∝FzD, z＝0.45. Its size distribution is lognormal, independent of fission density. In the selected range of fission density, the average size of void increases with the fission density increase, which is approximately in the range of 2.20 nm. The number of vacancies, porosity, swelling and fission density are positively correlated, while the void concentration slowly decreases to a stable value after it rapidly increasing with fission density. The number of vacancies varies roughly from 10² to 10⁶ during simulation. When the fission density is 14×10²⁰ cm^-3, the void concentration is about 1.6×10¹⁶ cm^-3, porosity is about 0.1, and the swelling of fuel volume shall not exceed 3%. The simulation results are basically consistent with the experimental values.