Objective To detect the expression level of exosome PD⁃L1（ePD⁃L1）in the plasma and tissue space of patients with gastric cancer and to explore the relationship between its expression and clinicopatho⁃ logical features，while to evaluate its diagnostic value in gastric cancer. Methods Forty patients with gastric cancer admitted to our hospital from December 2021 to December 2022 and 20 healthy control cases were selected. Plasma exosomes were purified and identified，and plasma ePD⁃L1 expression was determined by enzyme⁃linked immuno⁃ sorbent assay（ELISA）. During the same period，10 gastric cancer tissues and paracancellular tissues were collected to determine the expression of ePD⁃L1 in the intertissue space and verify the origin of plasma ePD⁃L1. The relation⁃ ship between ePD⁃L1 expression and clinical data was analyzed，and the diagnostic efficacy of EPD⁃L1 was evaluat⁃ ed by receiver operating（ROC）curve. Result Plasma ePD⁃L1 expression in gastric cancer patients was signifi⁃ cantly higher than that in healthy patients（P < 0.001），and its high expression was significantly correlated with CA19⁃9，tumor size，invasion depth，lymph node metastasis，and pTNM staging（P < 0.05）. Pearson correlation analysis showed a significant positive correlation between ePD⁃L1 expression in plasma and tissue（r = 0.7315，P = 0.0162）. The area under ROC curve（AUC）was 0.796（95%CI：0.658 ~ 0.935，P < 0.001）. Conclusion The expression of ePD ⁃L1 is associated with the progression of gastric cancer. There is a positive correlation between plasma and tissue ePD⁃L1 expression. Plasma ePD⁃L1 has certain diagnostic value in gastric cancer.