Grain evolution dynamics of ZnO nano-crystals under high temperature and pressure was studied on a cubic high pressure apparatus. The structure, grain sizes and morphology of the samples were characterized by X-ray diffraction and field emission scanning electron microscopy. It were found that the velocity of grain growth increased at first and then decreased with increasing the pressure below the temperature 300 ℃ (including 300 ℃). The grain sizes of the samples increased from 1 to 3 GPa and decreased from 4 to 6 GPa. The activation volumes at 300 ℃ from 1 to 3 GPa and from 4 to 6 GPa were calculated using the phe-nomenological kinetic grain growth equation, which are about －5.82 and 9.66 cm³/mol, respectively. Above the temperature 400 ℃ (including 400 ℃), grain sizes of the samples increased with in-creasing the pressure from 1 to 6 GPa.

Key words: nano-crystals ZnO, high temperature and pressure, grain evolution dynamics