The present invention relates to artificial crystal technology, and is large size potassium fluoroboroberyllate crystal and its hydrothermal growth process and frequency conversion device. During the hydrothermal growth process of potassium fluoroboroberyllate crystal, the selected mineralizer is hydroxide, carbonate, halide, borate or their optional mixture. The hydrothermal potassium fluoroboroberyllate crystal growing process has lumpy growth, rather layer growth, of the crystal plane and grown crystal with thickness over 5 mm. |