In this work, solubilities and physicochemical properties including pH, density, and refractive index were studied by the isothermal dissolution equilibrium method for the ternary system BaO-P2O5-H2O at 323.2 K. The obtained ternary phase diagram contained seven invariant points, five univariant curves, and five crystallization regions, corresponding to Ba(OH)(2)center dot 8H(2)O, [Ba-5(PO4)(3)(OH)center dot(BaHPO4)(1.5)], [Ba-5(PO4)(3)(OH)center dot(BaHPO4)(8.5)], BaHPO4, and Ba(H2PO4)(2), respectively. Those crystals were characterized by X-ray diffraction and scanning electron microscopy. The estimation models were obtained by fitting the univariant curves corresponding to the crystallization regions of BaHPO4 and Ba(H2PO4)(2). The properties including the refractive index, density, and mass fraction of P2O5 and BaO could be estimated by putting the pH into those models. The comparisons showed that the calculated values were in good coincidence with the experimental data. All the data and results obtained in this paper could be used to improve the desulfurization effect of wet-process phosphoric acid (WPA) and help WPA gradually replace thermal-process phosphoric acid.