Three experiments about KDP crystal were designed to analyze the relationship between the thin surface-layer growth mechanism and formation of solution inclusions. It is found that asymmetrical hydrodynamics condition and imperfect crystallographic shape can induce generation of a thin surface layer. The morphology of the thin layer is observed under microscopy and SEM, revealing that the thin surface layer was composed of many thinner layers. At the same time, the growth mechanism of thin surface layers was also found in the rapid growth of ADP crystal. (c) 2008 Published by Elsevier B.V.