Judgment of IAQ (Indoor Air Quality) has two kinds of methods to describe in general, objective and subjective. To consider the IAQ in underground engineering in objective, because of the low rate of ventilation, the special close space, the IAQ parameters (CO, CO2, HCHO, Radon, Organic and so on) in underground engineering are worse than that in above ground. In subjective, the parameters of heat, light and sound in underground engineering are also decrease man’s agreement rate. In order to make the IAQ in underground engineering in China, we get thousands of investigations of IAQ in underground engineering from about ten cities; these cities are distributed in different provinces. In this paper, we will analysis these investigations and describe the special IAQ characters of underground engineering.