Synthesis method of monocrystal diamond

The invention belongs to the technical field of diamond synthesis, and particularly relates to a single crystal diamond synthesis method which comprises the following steps: depositing a substrate on a single crystal diamond, and enabling a base table of a CVD (Chemical Vapor Deposition) device to be in full contact with a seed crystal substrate. The method comprises the steps that firstly, a crystalline diamond deposition substrate larger than 6 mm is taken, and the crystalline diamond deposition substrate is cut into a rectangular body with the thickness of 0.3 mm; by means of the high-flatness single crystal diamond seed crystal substrate, the seed crystal substrate and a base can make full contact and be added and stacked stably, the base is subjected to multiple times of cyclic growth, large-size single crystal diamond is obtained, splicing influences are avoided, the uniformity of crystals is high, and the uniformity of the crystals is high. And the temperature difference during the growth of the single