Low-pressure high-temperature annealing device and method for reducing stress of diamond

The invention belongs to the technical field of diamond single crystal growth, and relates to a low-pressure high-temperature annealing device and method for reducing diamond stress. The method comprises the steps that diamond is placed in an annealing device, the device is vacuumized for 2 h, and the vacuum degree is reduced to 10 mbar; and introducing Ar, enabling the vacuum degree in the device to be 10 -800 mbar, carrying out heat preservation annealing at 1500-1800 DEG C, and then slowly cooling to room temperature. The device comprises a cylindrical shell, an upper heat preservation cover and a lower heat preservation cover. A heating pipe is arranged around the outside of the cylindrical shell; a heat preservation and insulation layer is filled in the cylindrical shell; a cylindrical accommodating space capable of increasing and decreasing pressure is arranged in the heat preservation and insulation layer; a carbon material container is arranged at the bottom of the cylindrical accommodating