Abstract: Objective To explore the differences in species classification,abundance and diversity of intestinal flora samples between middle-aged and elderly people with phlegm-dampness and balanced constitution, and to find out the characteristic functional intestinal flora in middle-aged and elderly people with phlegm-dampness constitution, so as to provide the basis for the study of the relationship between phlegm-dampness constitution and metabolic diseases from the respect of microorganism. Methods People who went to department of TCM for diagnosis and treatment or medical examination center for physical examination in our hospital from May to December 2017 was selected as the study samples, and totally 30 persons with phlegm-dampness constitution and 30 persons with balanced constitution were included through the combination of TCM constitution identification software and professional syndrome differentiation. The fecal samples were collected and the total RNA was purified.The biodiversity sequencing was carried out by Miseq sequencing technology based on 16 SrRNA, and the species classification, abundance, diversity and differences between the two groups were analyzed by R(v3.1.1) software. Results ①The composition and relative abundance of intestinal flora were different among samples, but the main floras were Bacteroidetes, Firmicutes, Proteobacteria and Actinobacteria. ②The observed species, chao, ACE and shannon index of phlegm-dampness group were all smaller than those of balanced group(all P<0.05), and the simpson index was larger than that of balanced group(P<0.05). ③The relative abundance of Bacteroidetes(38.439±13.545) in phlegm-dampness group was lower than that in balanced group(46.669±12.984), while the relative abundance of Firmicutes(52.802±13.861) was higher than that in balanced group(45.742±12.990), and the difference was statistically significant(all P<0.05). Conclusion The species abundance and diversity of intestinal flora in people with phlegm-dampness constitution are significantly reduced. The relative abundance of Bacteroidetes decreasing and Firmicutes increasing are important structural features of intestinal flora in people with phlegm-dampness constitution.