Abstract: The radial migration of plutonium is one of the important performance characteristics of oxide fuels in liquid metal reactors. During the reactor irradiation, under the effect of the radial temperature gradient, plutonium in the fuel pellet migrates to the high-temperature region along the temperature gradient through the thermal diffusion mechanism. This leads to an increase in the concentration of fissile materials near the center of the fuel rod, thereby increasing the power at the center of the pellet and affecting the thermal performance of the reactor. In liquid metal reactors, due to the hard neutron energy spectrum and the sufficiently long neutron path, the fluence rate distribution at the pellet level is almost uniform, and the production rate of plutonium within the pellet is nearly the same. Since the liquid metal coolant has better heat-transfer performance, the linear power density of the pellet is usually higher, resulting in a larger temperature gradient within the pellet. The effect of plutonium migrating towards the center of the pellet will be more obvious and will become more concentrated as the burnup deepens. In this paper, the diffusion analysis of oxide fuel pellets was carried out through an fuel performance analysis program. The radial distribution data of plutonium isotopes under different fuel types, pellet structures, power densities, and burnup depths were obtained. Coupled with the Monte Carlo program and the heat-transfer model, physical and thermal-hydraulic analysis and calculations were performed to evaluate the influence of the plutonium migration phenomenon on the power distribution within the pellet and the thermal-hydraulic margin of the reactor. The oxide pellet analyzed in this paper is a UO₂ fuel pellet with a ²³⁵U enrichment of 19.75%, no central hole, a theoretical density of 10.96 g/cm³, and a nominal manufacturing density of 95% T.D. The pellet is in the fast-neutron energy spectrum of a typical liquid metal reactor. The research results show that the increase in linear power density and the decrease in thermal conductivity caused by the deepening of burnup are the fundamental reasons for the more prominent plutonium migration phenomenon under high power and deep burnup. This migration not only increases the power at the center of the pellet but also correspondingly reduces the thermal-hydraulic safety margin of the reactor. If there are pellets in the reactor core with an linear power density exceeding 300 W/cm and a burnup greater than 50 GW·d/tU, the potential impact of the plutonium migration phenomenon should be considered in the thermal-hydraulic safety analysis.