Objective：To investigate the effect and mechanism of down-regulation of programmed cell death ligand 1（PD-L1） expression on gefitinib-resistant（GR） non-small cell lung cancer cells. Methods：The expression levels of programmed cell death 1 （PD1） and PD-L1 mRNA and protein in non-small cell lung cancer cells were detected by RT-qPCR and Western blot. GR cells H1703/GR were obtained. Cell activity was detected by CCK-8. Western blot was used to detect PD1 and PD-L1 protein expression. Sh-PD-L1 was transfected into H1703/GR cells，cell activity was detected by CCK-8，apoptosis was detected by flow cytometry，and PI3K/Akt/mTOR pathway-related protein expression was detected by Western blot. PI3K/Akt/mTOR pathway activator IGF-1 was added，cell activity was detected by CCK-8 and apoptosis was detected by flow cytometry. Results：Compared with human immortalized lung epithelial cell line 16HBE，the expressions of PD1 and PD-L1 mRNA and protein in non-small cell lung cancer cell lines GLC82，A549，PC9，SK-MES-1，H1703，L78，H460，and H661 were all up-regulated（P<0.05，P<0.01），and H1703 cells were selected for subsequent experiments. Compared with H1703 cells，H1703/GR cells increased activity，and both PD1 and PD-L1 protein expressions were up-regulated（P<0.01）. Compared with GR group，GR+sh-PD-L1 group significantly reduced H1703/GR cell viability，increased apoptotic rate and decreased p-Akt/Akt and p-mTOR/mTOR protein expression（P<0.01）. Compared with GR+sh-PD-L1 group，the activity of H1703/GR cells in GR+sh-PD-L1+IGF-1 group was significantly increased and the apoptosis rate was significantly reduced（P<0.01）. Conclusion：Down-regulating PD-L1 expression enhances the sensitivity of non-small cell lung cancer to gefitinib by inhibiting activation of the PI3K/Akt/mTOR pathway.