Abstract: Blister thresholds of fuel plates are a standard to establish the safety margin for research and test reactors. The thresholds are determined by blister anneal test. In this study, a method was developed for simulating the blistering behavior of UMo/Zr monolithic fuel plates during annealing, and the influence of the number of internal fission gas atoms on the blister height was investigated. The evolution laws were obtained for the Mises stresses and the equivalent plastic strains in the cladding. The research results indicate that it is a critical reason for blistering that plastic strains occur in the cladding part surrounding the vacancy. This study lays a foundation for analyzing the mechanism and critical influence factors of blistering behavior.