Potassium chloride (KCl) as a new additive was added into the potassium dihydrogen phosphate (KDP) solutions in a small amount (5M%). The Solubility Curve and metastable zone width of KDP Solution with 5M% KCl were determined and we explained the mechanism of rapid growth of KDP-type crystals with KCl and NH4Cl as additives. respectively. The clear transparent crystal of KDP with a dimension of 54 x 54 x 42 mm(3) were grown rapidly by the cooling solution method in 2 days. KDP-type crystals grown were polished at face (001) for optical measurements. The transmission spectra. Raman spectra, electronic conductivity and the damage thresholds of the crystals were determined and compared. respectively. A new method to determine the deuterium content of DKDP crystal with thermogavimetric apparatus is developed in the article which implies the weighing of the initial material and products Of thermal decay. This handy method of analysis requires merely 30-50mg DKDP crystal sample to determine its deuterium content with high accuracy. (C) 2004 Elsevier B.V. All rights reserved.