<p>Graphene oxide (GO) is a promising candidate for enhancing cement-based composites, but stacking of GO is a negative factor that affects its enhancing capacity. This study aims to understand the impact of stacked GO on the interfacial structures and mechanical properties of cement-based composites from an atomistic insight. Structurally, it was observed that GO forms hydrogen bonds with surface-adsorbed water through its functional groups, which subsequently interact with calcium-silicate-hydrate (C-S-H) to create a cohesive structure. Additionally, stacked GO layers are interconnected through hydrogen bonds formed between their oxidized functional groups. During tensile and shear processes, interface failure primarily occurs between the stacked GO layers rather than at the interface between the GO layer and C-S-H. This is due to the relatively weak interlayer forces and lower interfacial energy dissipation capacity between the stacked GO layers compared to the GO/C-S-H interface. Mechanically, a monolayer of GO resulted in significant improvements in the mechanical properties of C-S-H, with the tensile strength, Young's modulus, shear strength, and shear modulus increased by 77.4%, 19.0%, 25.2%, and 7.6%, respectively. Conversely, stacked GO weakened the mechanical properties of C-S-H, with three GO layers causing a 38.5% reduction in tensile strength and a 14.6% reduction in shear strength. These atomic-level insights enhance our understanding of the interfacial structures and mechanical properties of calcium silicate hydrate reinforced with stacked GO.</p>