In this paper, the adsorption behavior of KOH, LiOH and Na2HPO4 by sodium silicate was simulated by Materials Studio. Besides, the quantity of the complex modifier (KOH, LiOH and Na2HPO4) was optimized by orthogonal test, and the effect of complex modifier on the properties of heat-hardened sodium silicate-bonded sand (SSBS) was analyzed. This research was conducted with sodium silicate as a part of two-component binder system where the second part was silica fume to be used for heat-cured sodium silicate-bonded ceramic sand. The results showed that the optimum quantity was 3% KOH, 0.6% LiOH and 3% Na2HPO4. The instant strength, 4 h strength, 24 h strength and the 800°C residual strength of the modified SSBS increased by 66%, 37%, 56%, and 27%, respectively. The modifiers were stably adsorbed on the surface of the sodium silicate at 298 K. Herein, Na2HPO4 and sodium silicate formed a composite structure, which made the formed bonding bridge dense, thus improving the tensile strength of SSBS at room temperature. During the process of heating at 800 °C and air cooling to room temperature, due to the reduced adsorption of water, the collapsibility of SSBS was reduced. [ABSTRACT FROM AUTHOR]