Human being is one of the results from the development of the nature. It is made up of many kinds of elements, and also is a system which chemical reactions cooperate with each other. Human body exchanges materials and energy with environment. Human survives demands many macroelements and microelements. Some microelements as Fe, Cu, Zn, Sr, F, I, Se and Si which can keep demands of normal mechanism of human being, if they are lack or over, people will fall ill, while some elements such as Cd which have no biological function will do harm to human being.