The synthetic process of MgxZn1-xO (0.30xxZn1-xO (x=0.4, 0.5, 0.6) are fabricated reproducibly by sintering mixture of ZnO and MgO powders under pressures of 4—5.6 GPa and temperatures of 1000—2000 ℃, and the problem of phase separation is solved. The MgxZn1-xO sample is characterized through several measurements of X-ray diffraction, scanning electron microscope, etc. The synthetic mechanism of cubic MgxZn1-xO is clarified and the phase diagram between temperature and components of MgxZn1-xO is obtained based on the experimental results.