N2S2-CBMBC, an N2S2 bromo-benzyl ether derivative, acts as a ligand and use 99m Tc-labelled complexes 99m Tc-N2S2-CBMBC can be used as an imaging agent to be applied to the aspect of detecting PD-L1 expression, realize the real-time, comprehensive and convenient detection of the PD-L1 level of tumors, and overcome the defects of an immunohistochemical method.