CVDZnSe and CVDZnS have similar crystal structure and properties,but absorption peak near 6.2 μm which is brought by the Zn-H is an important difference between as-grown CVDZnSe and CVDZnS. The H comes from the undissociated reaents that contain H.The reason why only ZnS has the absorption peak is discussed by comparing their deposition parameters (temperature, pressure), deposition rate and dissociated temperature of reagents that contain H. Because the dissociate temperature of H2Se is lower than H2S, the higher deposition temperature decreases the Zn-H in ZnSe, at the same time, the influence of Zn-H on ZnS can be decreased by increasing the deposition temperature. Lower deposition pressure of ZnSe is the other reason. Low pressure decreases the reactant concentration, furthermore it favors undissociated H2Se going back to the main airstream.