Abstract: Objectives To know the condition polluted by air microbes in the dorms of college students,and to find the factors that influencing gross bacteria in the air of college students' dorms, in order to provide the basis for promoting the air quality of students'dorms. Methods Natural sedimentation was adopted to monitor grass air bacteria in 96 dorms at the new campus of Tibet University. Results The gross air bacteria over-standard rate was 17.71% in the dorms of college students at Tibet University.The gross air bacteria of the afternoon was 944(553-1 573)cfu/m³,which was more than that of the morning 472(157-1 376)cfu/m³.The gross air bacteria over-standard rate of boys'dorms was 27.08%,which was higher than that of girls' dorms(8.33%). The gross air bacteria over-standard rate in good condition of sense health was 3.45% better than that in worse condition of sense health (38.89%). With the improvement of the sense health,the gross air bacteria over-standard rate was reduced(r_s=0.314,P=0.002).The gross air bacteria over-standard rate in dorms that have green plants was 6.25% better than the dorms without green plants (23.44%). There was more pollution by air microbes when there was a peculiar smell in the dorms.On the different floors, the gross air bacteria over-standard rate in dorms of college students can be decreased with storey.The higher you live in, the lower the gross air bacteria over-standard rate in dorms of college students was (r_s=-0.329,P=0.001). Conclusions The gross air bacteria over-standard rate of college students relate to sex,storey,time,condition of sense health,whether existing peculiar smell and putting green plants.We should adopt comprehensive control measures to reduce the gross air bacteria in the dorms of college students.