Abstract: high quality diamond crystals were synthesized in SPD6*1200 cubic apparatus, using a special technique that is, the synthesis pressure increased up to diamond nucleating pressure firstly, then decreased into the metastable region of diamond. Scanning electro microscope (SEM) results indicated that, diamond defects got decreased obviously and the morphology of diamond was much better than that synthesized by traditional technology. The size of diamond synthesized in metastable region was compared with diamond synthesized by traditional technology. The comparison results showed that the particle size of diamond was smaller, namely, the growth rate of diamond in metastalbe region got slower with the pressure decreased. Finally, diamond synthesizing mechanism of the new and traditional technology was discussed.

Keywords: high-pressure and high –temperature V shape region diamond