Abstract: The dissolving and crystallization process of zinc oxide in an alkalescency system like the hydrometallurgical process of alumina was discussed according to the equilibrium phase diagram of the Na₂O-ZnO-H₂O ternary salt-water system at 25,75 and 100℃ by the isothermal solubility method.The results show that the circulation of zinc oxide can be realized by separating zinc oxide through diluting if the mass fraction of sodium oxide is below 34% at 100℃.But for the equilibrium system in which the mass fraction of sodium oxide is above 29% at 100℃,it is also possible to separate sodium zincate by cooling.Sodium zincate can easily decompose into zinc oxide by diluting with water,and the circulation of zinc oxide is realized in this concentration range of sodium oxide.