Abstract: Knowledge of atmospheric water vapor are related to many aspects such as rainstorm forecast,preventing and managing of droughts and floods,protecting and improving of ecology and environment and so on.Now these knowledge are scattered in every branch of meteorology,and there is not theory framework about atmospheric water.From the viewpoint of earth water science,the branch of atmosphere water is short of.We suggest that a branch of atmospheric hydrology should be established to fill the theory gap.Atmospheric hydrology is knowledge systems on researching exist,motion,change,effect and utilize of atmospheric water.