Objective To Evaluate the environment quality in underground construction site based on the measurement of atmosphere composition and microclimate. Method Concentrations and composition of gases were analyzed by combined detection with mass spectrometer and gas chromatograph. Microbial content was detected by striking method. A microclimate model was built based on the measurements of temperature, humidity and wind speed in two years. Result Concentrations of inorganic gas was higher than national standard. Total volatile organic compounds were in the range of 4～6 mg/m3, which highly exceeded the national standard. Concentration of O2 descended obviously at the time when personnel went into the construction site, and was lower than the national standard of 299 mg/m3 after continuous working for 3 h. When an aerator was started, the average noise level was in the range of 70～93 dB, which was higher than the national standard(55～70 dB). In the course of working, the average microbial content reached 4 000 cfu/m3 which was 3 times as high as the background level. The microclimate characteristic with high humidity, low temperature and inadequate sunshine was unsuitable for dwelling. Conclusion Environment in the underground construction site is unfavorable as compared with that on the ground. The physiological function of working staff may be influenced obviously due to cumulative effect of the above mentioned factors, and may lead to aprosexia, hypomnesis, fatigue, etc. Six kinds of protection means are suggested in the paper.