Objective To explore the mechanism of the "exterior-interior relation between lung and large intestine" from the micro-ecology. Methods Forty Wistar rats were randomized in blank control group

lung disease group （allergic asthma）

bowel disease group （constipation）

and lung-intestine disease group （allergic asthma and constipation）

with 10 in each. The bronchoalveolar lavage fluid and fecal samples of all rats were collected for determining the main microbial types and contents of lung and intestinal flora and analyzing the basic features of micro-ecological condition in the lung disease

bowel disease

and lung-intestine disease. Results Compared with the blank control group

lung flora of the lung disease group and lung-intestine disease group were significantly different （P<0.01）

the intestinal flora of all the three group showed a significant difference （P<0.01）; the lung flora of the bowel disease group presented a significant difference （P<0.05 or P<0.01） compared with that of lung disease group. Under the condition of lung and intestine being both diseased

the lung flora of rats was significantly different in comparing with that of lung disease group （P<0.01）

and the intestinal flora was also significantly different in comparing with that of bowel disease group （P<0.05 or P<0.01）. Conclusion The lung disease may cause the changes in intestinal flora

and the bowel disease may also affect the changes in lung flora. It provides some experimental bases from micro-ecology for the "exterior-interior relation between lung and large intestine".