In order to address the issues of long setting time, low early strength, and poor impermeability of ordinary shotcrete, performance improvements were made by incorporating nano calcium-silicate-hydrate (C-S-H) gel. The effects of nano C-S-H gel on the setting time, compressive strength, and impermeability of shotcrete were investigated. Techniques such as hydration heat tests, X-ray diffraction(XRD), and scanning electron microscope (SEM) were used to explore the mechanisms by which nano C-S-H gel enhanced shotcrete performance. The results show that nano C-S-H gel significantly reduces the setting time of cement paste with an accelerator. Compared to the control group, shotcrete with 2% nano C-S-H gel exhibits a 19.0% increase in 1-day compressive strength and a 31.4% reduction in water penetration depth. Mechanistic analysis indicates that the nucleation and filling effects of nano C-S-H gel promote cement hydration and densify the internal structure of the concrete, thereby enhancing the overall performance of the shotcrete.