Double Network Hydrogels are polymer materials composed of two interpenetrating or semi-penetrating three-dimensional networks, and their unique contrast interpenetrating network structure and adjustable network crosslinking method overcome the obstacles in mechanical properties of single-network hydrogels, and are widely used in tissue engineering, intelligent sensors, ion adsorption and other fields with their good mechanical, anti-swelling, self-healing and other mechanical properties. However, the existing technologies suffer from numerous synthesis steps, complicated preparation conditions and the use of toxic and harmful chemical cross-linking, which limit the mass production of double network hydrogels for applications. Therefore, in recent years, the modification of double network hydrogels has received more and more attention, and researchers have carried out a series of structural modification studies mainly around how to improve the mechanical properties of double network hydrogels, aiming to broaden their application in various fields. In this paper, the types of double network hydrogels are reviewed, and the preparation methods, structures and unique properties of different hydrogels are introduced in detail. The research on modification to improve mechanical properties, anti-swelling performance and self-healing properties is analyzed, aiming to break through the current limitations of double network hydrogels and provide ideas and directions for their future development.