Abstract: To accurately predict the structural safety behavior of Lianghekou ultra-high core rockfill dam under full reservoir operation, a multi-objective back analysis of dam deformation and pore water pressure was conducted based on monitoring data. The study considered multiple factors, including instantaneous deformation, rheological effects, and wetting deformation of rockfill materials, within a fluid-solid coupling computational framework to determine constitutive model parameters and predict long-term dam deformation and pore pressure distribution. The results showed that the deformation and pore pressure values obtained from the back analysis aligned well with field measurements. The dam exhibited high construction quality, with good compaction of the core wall. The deformations of the core wall and rockfill zones were well-coordinated, and the overall deformation distribution was reasonable. Due to consolidation, wetting, and creep effects, the settlement at the dam crest continued to increase over time, but the rate of increase gradually slowed down. Meanwhile, the excess pore water pressure dissipated year by year. The findings can provide a reference for the structural design and long-term safety control of similar ultra-high rockfill dams.