Objective To investigate the distribution of air microorganisms in soldies′living quarters of one under-ground tunnel during airtight survival training .Methods Anderson sampling was carried out in Area A and Area B ( living quarters) and Area C (a toilet) at designated time and place.After sampling, the culture and identification of microorgan-isms were finished .Results ①In the living quarters of the whole underground tunnel , the total number of bacteria ranged from 125 to 37 800/m3,but it was 2692, 1844 and 2199/m3, respectively in Area A, B and C.The mean number of bac-teria was 2245/m3 .The number of fungi ranged from 0 to 10 017/m3 .The total number of fungi of Area A , B and C was 1064 , 883 and 1011/m3 .The mean number was 986/m3 .②The number of bacteria in the living areas presented three fea-tures:the total bacteria showed overall three peaksin Area A and B, buttwin peaksin Area C.In Area A and B, the number of bacteria exhibited low colony at first but fluctuated heavily later .In Area C, it decreased gradually to the mini-mum,and the fungi showed a wavy and irregular trend .③The air microbial species included cocci ( Micrococcus, Coriolis of Staphylococcus aureus, S.epidermidis and S.equorum) , bacilli ( Acinetobacter baumannii, A.lwoffii and Alcaligenes faeca-lis),and fungi (Mucor and Saccharomyces).Conclusion Although the content of microorganisms was up to the military hygiene standards , it was higher than in the same kind of tunnels .Themulti peakphenomenon of microbial distribution suggests that the change of air microorganisms in tunnels has its own characteristics .Most of the air microorganisms are con-ditioned pathogens that may cause illness if they are not under control .