Gastric cancer (GC) is a globally prevalent malignancy with a high propensity for peritoneal metastasis (GCPM), which is associated with a poor prognosis. The omentum, particularly its adipose tissue, plays a critical role in GCPM, but the underlying mechanisms are not fully elucidated. We conducted a multi-omics study, integrating lipidomics, proteomics, and metabolomics, using a co-culture system of omentum adipocytes and gastric cancer cells to investigate the molecular mechanisms of GCPM and identify therapeutic targets. Our analysis identified differentially expressed transcripts, proteins, and metabolites implicated in lipid metabolism and other biological processes. Functional enrichment analysis highlighted the involvement of these molecules in pathways such as fatty acid metabolism and phospholipid metabolism. A ceRNA network was constructed to reveal non-coding molecular regulatory mechanisms. Integrative analysis pinpointed core genes, proteins, metabolites, and potential biomarkers AGPAT2, HACD1, and ME1, which were significantly associated with GC prognosis.