Abstract: Changheba core wall rockfill dam 240 m in height is located on thick alluvium deposit. A grouting gallery is arranged at the top of the underground cut-off wall to connect the foundation diaphragm with the impervious dam core. This kind of gallery is subject to complicated loads, and some galleries have already been cracked and leaked in actual similar projects. Based on the sub-model method, three-dimensional nonlinear finite element analysis is performed to study the stress and deformation behaviors of the foundation gallery and cut-off wall. The thin-l ayer element is used to simulate the contact surfaces. The filling material s of this dam and alluvium deposit are simulated by means of the Duncan hyperbola <>E-<>μ constitutive model. Meanwhile the actual dam construction process and reservoir impounding process are considered as well. The results demonstrate that the longitudinal stress of the gallery is quite high for the lack of transverse joint along the riverbed sections and the stress extremum appears on the one-fourth section at both sides. The high transverse tensile stress will cause longitudinal cracks at the bottom of gallery. The structural joints between the galleries in riverbed and abutments have complex relative deformations in three directions and as a result, it's difficult to design the joint seal. Therefore the structural style of the gallery should be improved and some engineering measures need to be adopted to ensure the safety of the seepage control system of the dam.