Programmed cell death protein 1(PD-1)/ programmed death-ligand 1(PD-L1) are important immune checkpoint molecules leading to tumor immune escape.Blocking PD-1/PD-L1 can reactivate the killing effect of cytotoxic T cells on tumor, which is an important way of tumor immunotherapy.The expression of PD-L1 in tumor cells may affect the clinical efficacy of anti-PD-1/PD-L1 therapy.Therefore, understanding the molecular mechanism of PD-L1 expression regulation is helpful to guide the clinical application of PD-1/PD-L1 related immune checkpoint inhibitors.Regulation of PD-L1 expression involves chromatin and genomic changes, transcriptional and post transcriptional regulation, translational regulation and post translational modification.In addition, various factors in tumor microenvironment can also induce the expression of PD-L1 in tumor cells.This review systematically discussed the mechanism of PD-L1 regulation in tumor and analyzed its significance for tumor immunotherapy.