A thermodynamic model for the ion-exchange reaction process from potassium tetratitanate (K2Ti4O9, or expressed by K2O.4TiO(2)) fibers (Bao et al., 2002) was applied to the synthesis of derivatives of K2Ti4O9 fiber through the hydration process, including H2Ti4O9.1.2H(2)O, TiO2 fiber, K2Ti8O17 fiber and K2Ti6O13 fiber. A novel viewpoint was proposed that the Ti/K mole ratio (R) of the target products was taken as the controlling aim of the composition of hydrate intermediates in the hydration process. Based on this, the model was successfully used to predict the suitable conditions for the synthesis of phase-pure products. In the ion-exchange reaction process, the composition or hydrate intermediates was quantitatively controlled by the method of adjusting the pH value and K+ concentration with ion selective electrodes (ISEs).