【Abstract】 Objective To investigate the effect of pemetrexed on the expression of PD-L1 in human lung adenocarcinoma cell line hcc827 and its possible mechanism. Methods Hcc827 cells were treated with different concentrations of PEM (0,0.01,0.1,1,10,100 μmol/L) at different time (12,24,48 h). CCK-8 method was used to detect the proliferation inhibition of hcc827 cells. The IC50 was determined as the drug concentration in the follow up experiment, and the optimal action time was selected as the intervention time. Flow cytometry was used to detect the effect of different concentrations of PEM on PD-L1 The expression of the protein was influenced by the expression; Experimental group: control group (adding culture medium) and experimental group (IC50 PEM and PI3K / Akt pathway activator 740y-p were used alone or in combination) ,The expression of Akt and p-Akt protein in each groμp was detected by Western blotting; the effect of each group on the expression of PD-L1 in hcc827 cell line was detected by flow cytometry. Results Compared with the control group, PEM inhibited the proliferation of hcc827 cells in a concentration dependent manner (P＜0.05), and the difference was statistically significant (P＜0.05). The inhibitory effect of pemetrexed in 48h group was stronger than that in 12h group (P＜0.05), and there was no significant difference between pemetrexed and 24h group. With the increase of drug concentration, the expression of PD-L1 on the cell surface of each experimental group decreased gradually, which was significantly lower than that of the control group (P＜0.05). Compared with the control group, the expression of pAkt/GAPDH in the PEM group was significantly decreased. There was no significant difference in Akt/GAPDH between the two groups (P＞0.05) .Compared with the control group, the expression of PD-L1 increased in 740yp group (P＜0.05), decreased in IC50 PEM group and IC50 PEM+740y-p group (P＜0.05), and the expression of PD-L1 in IC50 PEM group was lower than that in IC50 PEM+740y-p group (P＜0.05). Conclusion PEM can down reulate the expression of PD-L1 in hcc827 cells which may be related to the inhibition of PI3k/Akt signaling pathway.