PEGylation agents are used to improve the pharmacokinetic properties of drugs or other biomolecules by attaching PEG to them. PEG is a non-toxic, non-immunogenic polymer with high hydrophilicity and flexibility that can increase the solubility of molecules and reduce renal clearance, thereby prolonging the circulation time of drugs in the body. PEGylation agents provide an effective way to improve the pharmacokinetic properties, stability and biocompatibility of drugs in drug delivery systems.