After the specific binding of programmed death-1 (PD-1) to programmed death ligand 1 (PD-L1) , the PD-1/PD-L1 complex can exert a co-suppressive/co-stimulatory immunoregulatory effect, which can inhibit the activation and proliferation of T cells and their cytokine secretion, and play a key role in tumor immunity, autoimmunity and immune tolerance. This review summarizes structures and regulatory mechanisms of the PD-1/PD-L1 signaling pathway, aimming to facilitate the understanding of immune pathogenesis of idiopathic inflammatory myopathies complicated by malignant tumors, and to seek potential therapeutic targets and diagnostic strategies.