Abstract: High earth-core rockfill dams (ECRDs) are characterized by complex stress paths, wide confining pressure ranges, and markedly different mechanical behaviors between the rockfill and the core material, leading to highly complex mechanical responses during construction and reservoir impoundment. The widely used Duncan-Chang model often exhibits significant inaccuracies—particularly in predicting horizontal displacements—while elastoplastic constitutive models typically require numerous parameters with unclear physical meanings that are difficult to determine, significantly limiting their engineering applicability and wider application. In contrast, the UH model features physically meaningful parameters that can be determined directly from conventional tests, enhancing its practicality; however, studies on its adaptability to deformation analysis of ultra-high core rockfill dams remain scarce. In this paper, a 3D UH model was integrated and implemented on the high-performance computing platform Geodyna 8.0. To account for the creep characteristics of rockfill materials, creep and its associated hardening effects were incorporated into the model, and numerical simulations were performed on the full construction and impoundment processes of the Lianghekou Project, China's first 300-m-class earth-core rockfill dam. The simulation accurately captures the spatiotemporal evolution of deformations in both the rockfill zone and the core zone, reproducing settlement and horizontal displacement distributions with high fidelity, and representing the mechanical behavior of rockfill and core material under a wide range of confining pressures and complex stress paths. The results demonstrate the validity and engineering applicability of the UH model formulation and its numerical implementation, thereby establishing it as a reliable tool for the numerical simulation and safety assessment of high earth-core rockfill dams.