The chemical structure and performance characteristics of cross-linker agents（inorganic/organic titanium，zirconium， boron，etc.） commonly used in hydro-fracturing fluid system was described，and the cross-linking mechanisms，technical indicators and field applications of organic boron cross-linker in hydro-fracturing fluid system with hydroxypropyl guar gum as the thickener agent was highlighted. Additionally，as for the aspect of the molecular structures，organic-ligand compositions， cross-linking properties，synthetic routes of different cross-linkers，it was explained that the cross-linking properties was codetermined by coordination center，pH of fracture fluid，ligands，thickener type and concentration. In addition，cross-linkers progress on both theory and field applications was mentioned and the applications status in extreme conditions，performance indicators，composite systems and economic in hydro-fracturing fluid was prospected.