An immunosuppressive agent having the structure of formula (I), a preparation method therefor, and pharmaceutical use thereof. A series of the compounds have strong inhibitory activity on PD-1/PD-L1 interaction, can be widely used for preparing medicaments for preventing and/or treating cancers or tumors, immune-related diseases and disorders, communicable diseases, infectious diseases or metabolic diseases mediated by PD-1/PD-L1 signaling pathway, and is expected to be developed into a new generation of PD-1/PD-L1 inhibitors.