PD-1/PD-L1-IN 3 TFA, a macrocyclic peptide, is a potent and selective inhibitor of the PD-1/PD-L1 and CD80/PD-L1 interactions extracted from patent WO2014151634A1, compound No.1. PD-1/PD-L1-IN 3 TFA interferes with PD-L1 binding to PD-1 and CD80 by binding to PD-L1, with IC50s of 5.60 nM and 7.04 nM, respectively. PD-1/PD-L1-IN 3 TFA can be used for the research of various diseases, including cancer and infectious diseases.