Abstract: In this paper, the important effection of water in living action is described. On the base of research for the actions of millimeter waves on water, and the analysis of molecular resonance mechanism of MMW actions on water, the important action of water resonance line in transport process of MMW in body is discussed, and the mechanism of MMW actions on living is clarified. This paper established an important theoretical basis for research on the mechanism of biological effects of MMW.