Abstract: The normal growth rate of KDP prismatic faces was measured in real time using laser- polarization- interference technique. Effect of supersaturation control on the real time measurement of dead zone of KDP prismatic faces was studied. It was found that the birefringence variation with temperature affected the dead zone curve. The dependence of face growth rate and dead zone on supersaturation was studied with solutiens of different impurity antents and different saturation temperature. The growth kinetics was further discussed with C-V model and K-M model. The relationship between optical quality and growth rate was discussed. It is considered the dead zone related to traditional temperature-decreasing method and the linear zone related to rapid growth method, respectively, should be confi