Cross-linking agents are widely used to modify nucleic acids, drugs and polymers. The same principle applies to protein modification and labeling. Based on factors such as reactivity and spacer length, the reagents used for cross-linking are divided into different types, each with its own specific functions and applications. Chemical crosslinking is mainly formed by covalent bonds. The cross linker may be hydrophobic to allow access to the hydrophobic protein domain, either through the cell membrane, or hydrophilic, to limit cross-linking to the water chamber. CXMS, a chemical cross-linked peptide identification technique based on biological mass spectrometry, can provide rich experimental information for the study of protein folding and protein-protein interaction.