Abstract: The crystallization metastable zone width numbers of potassium dihydrogen phosphate（KDP） solution with  different contents of Fe（Ⅲ） were determined by laser light scattering method.Effect of Fe（Ⅲ） with different contents on crystal growth rate of KDP was studied.Effects of Fe（Ⅲ） on the crystallization morphology，bulk density，and Fe（Ⅲ） content of the KDP crystals were investigated by means of batch crystallization process and without crystal seed added in the system.Results showed that with the increase of Fe（Ⅲ） content，the metastable zone of KDP was widened and the growth rate decreased；the KDP crystal morphology changed from regular prism to speculate，the cracking of the crystal happened，and the luster of the crystal became uneven；and the crystal bulk density decreased and Fe（Ⅲ） content of the KDP crystals in- creased gradually.

Key words: Fe（Ⅲ）, potassium dihydrogen phosphate, crystallization, separation and purification technology