Investigating the impact mechanisms of nano-C-S-H seeds early-strength agent on the early hydration of cement is pivotal for advancing their application in practical engineering. By comparing mechanical properties and hydration heat tests, the effect of varying content of synthesized nano-C-S-H and the differences in effects compared to commonly early-strength agents were analyzed. Additionally, XRD, TG-DTG and SEM were employed to elucidate the effect of nano-C-S-H on the cement hydration process. The results demonstrate that increasing the content of the synthesized nano-C-S-H seeds early-strength agent leads to an initial rise in 1 d compressive strength, hydration heat release rate, and total hydration heat, followed by a decline. The optimal early-strength effect is observed at content of 0.6% by mass of the cementitious materials. When the content of nano-C-S-H is 0.6%, the nano-C-S-H seeds early-strength agent has the best early-strength effect and has no negative effect on the compressive strength at 7 and 28 d. Compared to the blank group, the addition of nano-C-S-H significantly enhances the hydration rate during the cement induction period, as well as the formation and density of AFm, AFt and C-S-H gels during the 1 d age, but has no significant effect on the formation of hydration products at the middle and late ages.