The irradiation swelling caused by fission gas can promote UO2 fuel cladding contact and reduce fuel thermal conductivity, which is a key behavior affecting fuel element performance. This article built a fission gas irradiation swelling model for different burn-up ranges based on rate theory. The model first proposed control equations for intra-granular gas, inter-granular gas and point defects under low burn-up. Then the control equations for intra-granular gas considering grain subdivision and non-equilibrium growth of grain boundary pores under high burn-up were given. Finally, a model for coalescence and coarsening of grain boundary pores was established. On this basis, COMSOL software was used to solve the control equations. The model was preliminarily validated using experimental data, and the predicted bubble size and porosity were in good agreement with the experimental results.