Potassium dihydrogen phosphate (KDP) crystal is the only nonlinear optical material used in the Inertial Confinement Fusion (ICF) program. It has been found that metal ions have important effects on the growth and properties of KDP crystals, and zinc ion is a kind of common impurity ion in KDP raw material and crystals. In this paper, KDP crystals with different Zn<sup>2+</sup> ion concentration were grown from aqueous solution by the “point seed” rapid growth method. The effects of zinc ion on the morphology and optical properties of KDP crystals were investigated. The results showed that the introduction of Zn<sup>2+</sup> ions could impact the crystalline perfection and optical properties of KDP crystals.