This paper summarized the necessities of mitigating radon inside buildings, the main way by which radon goes indoors, the principles of preventing and mitigating radon when low buildings are erected and the methods of rating the addresses of buildings. It gave a minute introduction of the methods or rules of mitigating radon in the process of designing and constructing low buildings in America. It also introduced at some length the research about the methods of mitigating radon inside the buildings which are fit for the condition of our country.