This article uses the hydrothermal method to prepare the high dispersion spherical ZnO powders, The phase composition and microstructures of powders were characterized by X-ray diffraction (XRD), scanning electron microscopy analysis (SEM). The influence to phase compose and the microstructure of ZnO powders were investigated with the forerunner fluid pH value, the hydrothermal response temperature. The growth mechanism of ZnO powders was explored in the alkaline environment. The result indicated: Under the alkalinity condition, ZnO crystalling phase do not change with the pH value, and is for spiauterite structure. When pH value was 8 approximately, the sole sphere ZnO powders are prepared, and the ZnO powders has good dispersivity, uniformed powder particle size distribution, and the particle size is about 1.5mm. The mechanism of forming sphere ZnO pellet is reduced the concentration of OH- ion in solution, and suppressed the growth speed of the fast growth direction, and caused each direction growth same speed.