To explore the structure of intestinal flora，intestinal microbial metabolism pathways and the characteristics of fecal short-chain fatty acids in patients with Yang deficiency constipation，so as to provide a basis for the diagnosis and treatment of Yang deficiency constipation.

Twenty patients with constipation due to Yang deficiency and 20 healthy volunteers were selected as the research objects. The 16S rRNA sequencing was used to analyze the structure of intestinal flora，gas chromatography-mass spectrometry was used to determine the levels of fecal short-chain fatty acids，and the correlation between significantly different flora and short-chain fatty acids was analyzed. Finally，the macrogene sequencing technology was used to analyze the differential metabolic pathways of intestinal microorganisms.

Compared with those of the healthy controls，the α diversity index of intestinal flora in the patients with constipation due to Yang deficiency was significantly increased and the β diversity was significantly changed. At the phylum level，the abundances of Fusobacteriota，Verrucomicrobiota and Bacteroidota increased significantly（P<0.05），while the abundances of Proteobacteria and Firmicutes decreased significantly（P<0.05）. At the genus level，the abundances of Parabacteroides，Ruminococcus and Collintella were significantly increased（P<0.05），while the abundances of Dialister，Fusicatenibacter，Roseburia，Bifidobacterium，Lactobacillus and Faecalibacterium were significantly decreased（P<0.05）. The levels of fecal acetic acid，propionic acid and caproic acid were significantly decreased（P<0.001），but the levels of butyric acid，isobutyric acid，valeric acid and isovaleric acid were significantly increased（P<0.001），and the correlation analysis results showed that there was a correlation between short-chain fatty acids and different flora. Functional analysis showed that the abundance of genes related to amino acid metabolism，carbohydrate metabolism，metabolism of cofactors and vitamins decreased significantly（P<0.05），while the abundances of genes related to translation and neurodegenerative disease increased significantly（P<0.05）.

The structure of intestinal flora，microbial metabolism pathways and fecal short-chain fatty acids in patients with Yang deficiency constipation changed significantly，which may be the important reasons for constipation.