The influence of graphene oxide (GO) incorporation on calcium silicate hydrate (C-S-H) molecular structure is a hot topic. This study uses molecular dynamics (MD) simulation to explore GO's modification effect on C-S-H. Two initial models, C-S-H and GO/C-S-H, are built, followed by processing and kinetic optimization. Uniaxial tensile simulation tests mechanical properties and studies damage and toughening mechanisms. Results indicate significant differences in C-S-H gel's action mechanisms in X, Y, and Z directions. GO only enhances C-S-H's tensile strength and elastic modulus in the Z direction. In the GO/C-S-H composite, GO and C-S-H attract each other. The locking between GO's oxygen-containing groups and C-S-H boosts interfacial load transfer and stops micro-crack expansion. Also, the deprotonation of GO groups and water dissociation form a hydrogen-bond network, improving the composite's strength and stability.