Objective：To investigate whether knocking down PD - L1 expression can enhance the effects of DC vaccine to treat pancreatic cancer. Methods：PD-L1 expression in normal pancreatic tissues and pancreatic cancer tissue specimens were detected by immunohistochemistry in tumor specimen of 42 pancreatic carcinoma patients respectively. A Panc-1 cell line with low PD-L1 expression established by lentivirus mediated RNA interference targeting PD-L1 was named Panc- 1/PD-L1- RNAi. At the same time，negative control cells Panc-1/LV-Control and wide type Panc-1 cell line was used in this study. These three groups of pancreatic cancer cells were co-cultured with CD8+ T cells and mature DC，and then IFN-γ production was detected by ELISA. Pancreatic cancer tumor-bearing hu- SCID mice model was established. DC vaccination was performed to investigate tumor inhibition effects. Results：Higher expressions of PD - L1 were detected in pancreatic carcinoma than in normal pancreatic tissue（P＜0.001）detected by immunohistochemistry examination. In the T cell reaction study，IFN-γ production is much higher in the PD-L1 knocking down group than that in the other two control groups（P＜0.001）. In vivo，PD-L1 knocking down combined with DC vaccination could significantly prevent tumor growth in the hu-SCID model. Conclusion：PD-L1 is expressed higher in pancreatic cancer than in normal pancreatic tissue. Suppressing PD-L1 expression in cancer cells during DC vaccination might be a more efficient strategy in immunotherapy for pancreatic cancer