The invention discloses a high-temperature and high-pressure hydrothermal kettle which comprises a foam metal crystallizing part and a hydrothermal reaction container, wherein the hydrothermal reaction container is arranged in a high-pressure kettle body; a dissolving area and a crystallizing area are positioned in the hydrothermal reaction container; the crystallizing area is provided with the crystallizing part which is favorable to crystal growth, and the crystallizing part is made of foam metal. According to the high-temperature and high-pressure hydrothermal kettle, a large quantity of nucleation sites which are suitable for crystal attachment are generated by arranging the crystallizing part made of the foam metal in the crystallizing area and utilizing the structural characteristics of high specific surface area and the like of the foam metal, compact mesh openings inside the foam metal can play roles in grabbing crystal grains and preventing the crystal grains from sliding to the dissolving area, so that the advantage that a metal wire and a metal sheet are taken as crystallizing supporting bodies in the traditional temperature-difference hydrothermal kettle is absorbed, the detects of small effective nucleation area, grown crystal grain dropping, excessively intense convection, transportation obstruction and the like are overcome, the crystallizing efficiency is improved to a great degree, the crystal grains are promoted to be further grown, and the crystal output is further increased.