Abstract: Microcosmic defects influence the optical properties and mechanical properties of CVDZnS effectively. In this article, the deposition technique was introduced and experiment methods such as SEM, TEM and metalloscopy were adopted to study the microcosmic defects such as unique large grain, columnar grain, micro-cracks, micro-poles and impurity. The microstructures of these defects were observed, at the same time the formation cause of these defects was analyzed. The main reason of the growth of unique large grain in CVDZnS was the high deposition rate. High reaction concentration, shield effect on substrate and Zn/H2S1 formed columnar grain which made the structure of CVDZnS loose. The lower deposition temperature increased growth stress in CVDZnS, brought bowing, made the grain blending and produced lots of micro-cracks in crystal. Micro-poles and impurity were made by high reaction concentration in local deposition chamber. So it is necessary to improve the gas flow in deposition chamber to make the concentration uniformly.