Antibody-drug conjugate (ADC) connects small molecule drugs with biological activity to the monoclonal antibody through a chemical link, and the monoclonal antibody acts as a carrier to target the small molecule drugs to target cells. And Fmoc-Val-Cit-PAB-PNP is a kind of linking agent, composed of 4 amino acids, and the N-terminal is protected by Fmoc, which is very stable.