Abstract: Different Zn salts including Zn(CH3COO)2·2H2O, ZnCl2, Zn(NO3)2·6H2O and ZnSO4·7H2O and different alkalies including NaOH and KOH were used as raw materials to produce the precursory solution Zn(OH)4^2-, and ZnO crystals were synthesized when Zn(OH)4^2- decomposed in hydrothermal environment. The phase identification, morphology and size of the products were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The anions of CH3COO^-, SO4^2-, NO3^- and Cl^- in the solution formed individually interfering ion pairs with Na⁺ at 170°C. The morphologies of ZnO crystals obtained along with their growth for 12 h are flake/ball-like aggregates, bloomy with obvious of unobvious polarity growth and small-size bloomy. In addition, the ion pairs formed individually by Na⁺, K⁺ and CH3COO^- at 140°C interfered the crystal growing and, after reacting for 12 h, they were prepared into flaky and needle-like ZnO nanocrystals. It could be known from the analysis of SEM images that different interfering ions in the solution have great effects on the morphologies of ZnO crystals. And the interference mechanism of the interfering ions was analyzed simply.