Azide-PEG-Mal (N3-PEG-Mal) is a linear heterobifunctional PEG polymer. Contains azide and maleimide groups at both ends, respectively, azide can be used for molecular conjugation by click chemistry, and maleimide can be reacted with thiol groups. Heterobifunctional PEG can provide good water solubility and is suitable for the development of antibody drug conjugates.