With high water content(～90 wt%) and significantly improved mechanical strength(～MPa),double network(DN) hydrogels have emerged as promising biomaterials with widespread applications in biomedicine.In recent years,DN hydrogels with extremely high mechanical strength have achieved great advance,and scientists have designed a series of natural and biomimetic DN hydrogels with novel functions including low friction,low wear,mechanical anisotropy and cell compatibility.These advances have also led to new design of biocompatible DN hydrogels for regeneration of tissues such as cartilage.In this paper,we reviewed the strategies of designing high-strength DN hydrogel and analyzed the factors that affect DN hydrogel properties.We also discussed the challenges and future development of the DN hydrogel in view of its potential as biomaterials for their biomedical applications. With high water content (~ 90 wt%) and significantly improved mechanical strength (~ MPa), double network (DN) hydrogels have taken as promising biomaterials with widespread applications in biomedicine.In recent years, DN hydrogels with extremely high mechanical strength great advance, and scientists have designed a series of natural and biomimetic DN hydrogels with novel functions including low friction, low wear, mechanical anisotropy and cell compatibility. these advances have also led to new design of biocompatible DN hydrogels for regeneration of tissues such as cartilage .In this paper, we reviewed the strategies of designing high-strength DN hydrogel and analyzed the factors that affect that DN hydrogel properties.We also discussed the challenges and future development of the DN hydrogel in view of its potential as biomaterials for their biomedical applications.