Regeneration process of a 330 x 330 x 20 mm(3) Z-plate seed is carried out in a 1.5 metric tonnage volume crystallizer that placed in a water bath of temperature fluctuation less than +/- 0.02 degrees C within 10 days. The surface of the whole crystal was restored by the formation of a box-like structure filled with growth solution, and then the transparent layer of perfect tetragonal KDP crystal without inclusions, crack and milky regions just like those produced by traditional slow cooling technique can be grown from solution. After the regeneration, the height of KDP crystal is merely 0.5 times the side of plate seed. We found it that the optical transmission and laser damage threshold of the KDP crystals we grown are not significantly different from those of KDP crystals grown by traditional method. (C) 2007 Elsevier B.V. All rights reserved.