The interactions between the electromagnetic field and the biology system can cause the variation in conformations organizations, function and other aspects of different biological targets. When domestic sewage disinfected subsequently by constant electromagnetic wave, the microcosmic molecule with certain electric dipole-moment and biopolymer that has dielectric properties in cell may cause dielectric wastage under the outward electromagnetic field. And thermally biological effect will be produce because the energy of the microwave can be transformed as the thermal energy of movement which makes biology system temperature risen. Under the effect of the electromagnetic field in addition, the variety of the velum’s voltage not only makes the structures of cell membrane change and the gates of K,+, Na,+, open but also makes the gates of Ca,2+, open depending on the voltage. A large amount of Ca,2+, out of the velum could come into the cell at the voltage grad and induce the dead of the cells, which cause the biological non-heating effect. The larger variety the membranaceous voltage, the more cells would die. It has been shown that microwave secondary disinfection is simple method with high efficiency, lower price, easy to automatization, no additional and no secondary pollution.