Objective To explore the characteristics of oropharyngeal metabolites of postoperative pneumonia (POP) and non-POP patients with gastric cancer by non-targeted metabolomics, and to provide reference for revealing the pathogenesis as well as clinical prevention and control. Methods Oropharyngeal swabs were collected from patients who underwent surgical treatment for gastric cancer in the department of gastrointestinal surgery of a tertiary hospital in Fujian Province from January 2022 to December 2023, nested case-control study was adopted, with 30 cases in POP group and non-POP group, respectively, ultrahigh performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) technique was adopted for detection, and multivariate statistical analysis was performed. Results The metabolites of POP group and non-POP group preoperatively, POP group and non-POP group postoperatively, POP group preoperatively and postoperatively, as well as non-POP group preoperatively and postoperatively did not show a clear trend of separation on the score graph of principal component analysis (PCA), partial least squares discriminant analysis (PLS-DA), and orthogonal partial least squares discriminant analysis (OPLS-DA), but the screening of the differential metabolites revealed that the relative abundances of ascorbic acid and lipoic acid in the POP group preoperatively were lower than non-POP group preoperatively. The relative abundance of 5’-adenylic acid in the POP group preoperatively was lower than postoperatively, while the relative abundances of succinic acid and phenylacetaldehyde were higher. There were differences in metabolic pathways such as phenylalanine. Conclusion Alteration of metabolite level due to abnormalities in specific metabolic pathways presents in the deve-lopment of gastric cancer POP and may be related to the development of POP.