Abstract: Objective To evaluate the effect of syndrome differentiation in traditional Chinese medicine on intestinal flora and metabolomics in elderly patients with community-acquired pneumonia（CAP）after discharge from the hospital. Methods Nineteen elderly patients with CAP（11 in the experimental group and 8 in the control group）who were discharged from from the First Affiliated Hospital of Henan University of Traditional Chinese Medicine between December 2022 and November 2023 and 16 healthy volunteers were randomly selected. Plasma and fecal samples were collected. The changes in gut microbiota were analyzed using 16S rDNA high-throughput sequencing technology. Plasma metabolomics research was conducted using ultra-high-performance liquid chromatography-mass spectrometry technology. Results Based on the intestinal flora assay,at the phylum level,the abundance of Campylobacter species and Desulfovibrio phylum was increased after treatment（both P < 0.05）；at the genus level,the genera of Fusiform streptococcus,Trichoderma sphaericornutum group NK4A136,Desulfovibrio unclassified,and Prevotella anomalies were significantly elevated（all P < 0.05）. Based on untargeted metabolomics assay,the treatment improved patients’ metabolite levels of L-tryptophan,malonate,and glycine,which are mainly involved in glycine,serine,and threonine metabolism,aminoacyl-tRNA biosynthesis,and purine metabolism pathways. In the joint analysis of intestinal flora and plasma differential metabolites,Patella species showed a significantly negative correlation with adenine after treatment（P = 0.006）；Fusobacterium spp. showed a significantly negative correlation with 4,6-dihydroxyquinoline（P = 0.003）；and Lactobacillus spp. showed a significantly positive correlation with adenosine phosphorothioate（P = 0.004）. Conclusions In post-discharge elderly CAP patients,syndrome differentiation in traditional Chinese medicine may exert therapeutic effects by improving the structure of intestinal microbial species,increasing the relative abundance of probiotics and decreasing the relative abundance of harmful bacteria,and influencing the pathways associated with the metabolism of amino acids,proteins and energy.