The Goupitan Project is characterized by huge flood discharge and high fall, therefore, the strong rainfall and fog flow caused by flood discharge will have influence on the safety of the project and the normal operation of the plant. By the research on physical model and empiric formula calculation, a deepgoing research is conducted on the phenomena of local rainfall in the downstream of the dam caused by atomization of flood discharge. On the basis of the study results, the characteristics of rainfall intensity are analysed and compared with those of the analogy projects. The measured data obtained in the physical model are basically accord with calculated results by an empiric formula.