Abstract: With the deep understanding of tumor immune microenvironment， people find that immune evasion of tumor cells is the main factor of tumor progression. PD-1/PD-L1 signal pathway is a negative immune costimulatory molecule found in recent years which plays an important role in tumor immune evasion. This review briefly summarizes the mechanism of PD-1/PD-L1 signal pathway in tumor immune evasion and research progress of their antibodies in the treatment of tumor， which may provide new ideas and methods for tumor immunotherapy.