Abstract: The measurement of KDP crystal growth rate is helpful to study on the effect of various factors on the growth of KDP crystal. In situ precise measurement of crystal growth rate and dead zone of
KDP prismatic faces was achieved by using laser-polarization-interference technique. The experiment result is affected by various conditions such as crystal dimensions. It is found that the seed crystal
of small dimensions is in favor of token on the dead zone. The dislocation etch pits produced when the solution temperature is higher than supersaturation point are considered to cause the abnormal
phenomena disturbing the measurement.

Key words: KDP, dead zone, growth rate, in situ measurement