Abstract: After the Fukushima nuclear accident in 2011, the international community has put forward higher requirements for the safety and reliability of new generation nuclear power plants and nuclear fuels. As an important measure to improve the safety performance, the development of accident tolerant fuel (ATF), which can tolerate accidents to a certain extent and has inherent safety, has become an important direction for the development of the nuclear fuel field. Due to the relatively low melting point of U₃Si₂, it can be used as a second phase to be mixed with UN for sintering, and the sintering temperature of pure UN can be reduced by taking advantage of the characteristics of liquid-phase sintering. U₃Si₂ phase can also stabilize the grain boundary interface of UN, and cause UN cracking mainly transgranular fracture. It can limit the exposure of the fresh surface and improve the water vapor corrosion resistance of the pellet to a certain extent. Therefore, UN-U₃Si₂ composite pellet has become a current research hotspot. In this paper, UN-U₃Si₂ composite pellet was studied systematically by spark plasma sintering combined with characterization methods, including microstructural observation, chemical composition test, thermomechanical and mechanical properties measurement. The effects of sintering temperature, holding time and sintering pressure on the densification of composite pellets were studied by orthogonal experiments. The influence of particle size on the densification of composite pellets was studied through the combination of different UN and U₃Si₂ powders. The effects of different U₃Si₂ content on thermal conductivity, hardness and compressive strength of composite pellets were studied by adjusting the mixing ratios, and the reason for the variation of thermal conductivity of the composite pellet with the mixing ratio was analyzed. The results indicate that the optimal sintering parameters for UN-20%U₃Si₂ composite pellet are sintering temperature of 1 650 °C, holding time of 30 min, and sintering pressure of 50 MPa. Under these conditions, the pellet density reaches 13.60 g/cm³, and the relative density is 98.30%. The significance of the influence on pellet density is sintering temperature>sintering pressure>holding time. The density of UN-20%U₃Si₂ composite pellet prepared by fine UN and coarse U₃Si₂ powders is the highest, which is 13.60 g/cm³, and the relative density is 98.31%. The UN-20%U₃Si₂ composite pellet has the best comprehensive performance, with thermal conductivity of 29.0 W/(m·K) at 900 ℃, thermal expansion coefficient of 8.90×10⁻⁶ K⁻¹ at 600 ℃, hardness of 637 HV1, and compressive strength of 331.0 MPa. The experimental results of this paper can provide a certain basis for the subsequent research and application of UN-U₃Si₂ composite pellet.