Abstract: Aiming at the problems of intricate structure, multi-stage processing, and stringent welding deformation control for the large rotating carousel of spent fuel dissolver, and utilizing a multi-scale simulation strategy of “refined local joint analysis with global structural mapping", this study simulates the evolution of residual stress and deformation distributions in the structure throughout a 8-stage welding and heat treatment process using the domestic welding simulation software YYF InteWeld. The simulation results indicate that significant deformation occurs during the welding of the bucket shroud to the backplate, and the ring plate to the bucket sideplate, with peak values reaching 8.7 mm. Furthermore, Stress concentration phenomena are observed at the weld seams throughout the global structure, with peak values reaching 310 MPa. To mitigate these effects, a comprehensive optimization scheme was developed focusing on,fixturing, and heat treatment parameters: additional fixturing was implemented at the bucket orifice, and the annealing soaking time was extended to 10-12 hours. This research predicts the evolution of residual stress and deformation distributions in the large-scale, complex structure during multi-stage processing. The simulation results provide a critical reference for process design, contributing to enhanced manufacturing precision, shortened R&D cycles, and reduced production costs.