This paper investigates the interface debonding behavior of graphene (G) on a calcium silicate hydrate (C-S-H) substrate using molecular dynamics (MD) simulations. The effect of interfacial water content on the debonding behavior of graphene on cement-based composites was studied. Simulation results reveal that there is only a van der Waals force between G and C-S-H; the interface bonding strength is weak; and the debonding properties (maximum peeling force (F_max) and work (W)) are low. The debonding energy of graphene decreases with an increase in interfacial water content, indicating that water intrusion will weaken the binding effect of G and C-S-H, and reduce the difficulty of graphene’s debonding on a C-S-H substrate. Exploring the adhesion behavior of graphene on C-S-H under the influence of humidity at the nanoscale is of great significance for understanding the basic adhesion mechanism, optimizing composite material properties, and promoting the development of related disciplines.