Carbon dots (CDs), as an innovative nanomaterial exhibiting superior dispersion properties and exceptional economic efficiency, display unique potential for application in regulating cement hydration. Nevertheless, the precise mechanism by which CDs affect cement hydration kinetics has yet to be fully elucidated. This research for the first time uncovers the impacts and regulatory mechanisms of CDs on tricalcium silicate (C3S) hydration utilizing a multiscale methodology that combines micro characterization with molecular dynamics (MD) simulations. Specifically, N-doped CDs (NCDs) are deliberately synthesized via a hydrothermal synthesis approach and showcase good dispersion stability within saturated Ca(OH)2 solution. Experimental findings show that adding 0.1 wt% NCDs reduces the hydration induction period of C3S by 0.9 h relative to pure C3S pastes, elevates the peak heat flow by 12 %, and substantially increases the Ca2+ concentration throughout hydration. Micro characterization analyses indicate that NCDs enhance both the formation and densification of calcium silicate hydrate (C–S–H), yielding a thicker layer of hydration products. Moreover, NCDs diminish the average silicate chain length within C–S–H while augmenting its structural disorganization. Mechanistic exploration elucidates that NCDs achieve dual modulation of the C3S dissolution-nucleation process, both by accelerating C3S dissolution and functioning as nucleation sites exhibiting strong adsorption toward silicate tetrahedral units through electrostatic and van der Waals forces. This work systematically clarifies the action mechanism of NCDs, offering fresh perspectives for advancing nano-modified cementitious materials.