There is an optimum gypsum content in supersulfate cement (SSC), although nano-SiO2 (NS) can effectively improve the strength of SSC, but it can inhibit the hydration reaction of gypsum and aluminum phase, and the optimum gypsum content is changed. So optimizing the content of gypsum in the system is expected to further improve the performance of SSC. In this paper, the effect of mixing with or without 3% (mass fraction) NS on the mechanical and microscopic properties of SSC with gypsum content (5.0%~15.0%, mass fraction) was studied. The results show that the overall strength of SSC without NS develops slowly, the strength shows a downward trend with the increase of gypsum content at 1 d, and the optimum gypsum content is 7.5%. When NS is added, the strength increases significantly, the 3~28 d strength increases 100%~200%， the optimum gypsum content shows an increasing trend and the maximum strength is obtained when the gypsum content is 15.0% (the maximum content designed in this paper). NS lags gypsum consumption rate and inhibits ettringite formation, but does not affect the final consumption of gypsum. After the addition of NS, the chemical binding water content and gypsum consumption of SSC show an increasing trend, indicating that the demand for gypsum in the system increases. By exploring the change of the optimal gypsum content in NS-modified SSC, this paper provides new ideas for further reducing the amount of mineral powder, and improving the green and low carbon properties of SSC.