In this paper,the diamond epitaxial growth mechanism has been studied in detail by employing several types of diamond as a seed in a catalyst-graphite system under high pressure and high temperature (HPHT) conditions.We find that the diamond nucleation,growth rate,crystal orientation,and morphology are significantly influenced by the original seeds.The smooth surfaces of seeds are beneficial for the fabrication of high-quality diamond.Our results reveal that the diamond morphology is mainly determined by the original shape of seeds in the early growth stage,but it has an adjustment process during the growth and leads to well symmetry.Additionally,we have also established the growth model for the twinned diamond grown on several seeds,and proposed the possible growth processes by tracking the particular shapes of seeds before and after treatment under HPHT conditions.These results suggest that the shape-controlled synthesis of diamond with well morphology can be realized by employing certain suitable diamond seeds.This work is expected to play an important role in the preparation of trustworthy diamond-based electronic and photonic devices. In this paper, the diamond epitaxial growth mechanism has been studied in detail by employing several types of diamond as a seed in a catalyst-graphite system under high pressure and high temperature (HPHT) conditions. We find that the diamond nucleation, growth rate, crystal orientation, and morphology are significantly influenced by the original seeds. smooth surfaces of seeds are beneficial for the fabrication of high-quality diamond. Our results reveal that the diamond morphology is primarily determined by the original shape of seeds in the early growth stage , but it has an adjustment process during the growth and leads to well symmetry. Additionally, we have also established the growth model for the twinned diamond grown on several seeds, and proposed the possible growth processes by tracking the particular shapes of seeds before and after treatment under HPHT conditions. the results of this result that the shape-controlled synthesis of diamond with well morphology can be realized by employing ce rtain suitable diamond seeds. This work is expected to play an important role in the preparation of trustworthy diamond-based electronic and photonic devices.