Programmed death protein-1 (PD-1) and its ligand, PD-L1, are critical immune checkpoints in tumors whose interaction negatively regulates the activation and proliferation of effector T cells, playing a crucial role in tumor cells evading immune surveillance. Blocking the binding of PD-1 to PD-L1 can relieve the inhibition of T cells by tumor cells or antigen-presenting cells, restoring their recognition and cytotoxicity against tumor cells. However, the expression of PD-L1 is intricately regulated and varies among different types of tumors, primarily occurring at genetic, transcriptional, and post-transcriptional levels. In this article, we review the regulatory processes involved in PD-L1 expression and its roles in tumor immunotherapy, which are of great significance in oncotherapy, as the focus of future research lies in achieving precise immunotherapy targeting tumors with distinct characteristics, guided by the regulatory mechanisms.