Radon is a kind of radioactive inert gas. It exits in the soil pore, the underground water and the air. Radon and radon daughters impair body. After they are inhaled into the lung, radon daughters decay, emit α-ray, lead to internal irradiation and even cause lung cancer. Radon can accumulate indoors; the problems of indoor radon concentration have caused attention. In this paper, the characters, sources, health effects of radon are discussed in detail.