Abstract: In order to deeply analyze the changing situation of nutrients during the fermentation of Dangshan pear juice by lactic acid bacteria, in this study, the ultra-performance liquid chromatography-mass spectrometry (UPLC-MS) was used to analyze the metabolomics changes during the mixed fermentation of Dangshan pear juice by Lactobacillus plantarum and Lactobacillus acidophilus. The sensory evaluation results indicated that the fermented pear juice exhibited a better balanced sourness and sweetness, along with a more complex aroma profile. The principal component analysis (PCA) results indicated that all samples could be clearly classified into three categories. A total of 80 differential metabolites were identified through metabolomics analysis, mainly including amino acids, peptides, sugars and organic acids. The results by KEGG pathway enrichment analysis indicated that these differential metabolites were mainly involved in some key metabolic pathways such as phenylalanine, tyrosine and tryptophan metabolism, starch and sucrose metabolism, fructose and mannose metabolism, glutathione metabolism, arginine metabolism, as well as the tricarboxylic acid cycle and pyruvate metabolism. The research results showed that lactic acid bacteria fermentation could significantly change the composition of metabolites in pear juice, promoting the biodegradation of complex macromolecular substances, thereby improving its nutrition and functional properties. This study provides a theoretical basis and technical support for the industrial production of fermented beverages from Dangshan sweet pears.