The results obtained here confirm that the hydration of $C_4AF$ (here on C: CaO, A: $Al_2O_3$, F: $F_2O_3$) was retarded by silicate ions in the solution. In practical terms, the solubility of $C_4AF$ was reduced by increasing amount of silicate ions in the solution of hydration. The hydration of $C_4AF$ did not occur in liquid with a high concentration of silicate ions. Therefore, the reason why the hydration of $C_4AF$ in Portland cement has low hydraulic reactivity is attributable to the high concentration of silicate ions during the hydration of Portland cement. And it was also found that due to the very stable and strong bonding of silica formed on the surface of the $C_4AF$ particle, $C_4AF$ has a low hydraulic reactivity in solution containing silicate ions.