Hydrogels are a series of soft and wet materials with three dimensions of crosslinked networks. Hydrogels have attracted great attention due to their diverse functional properties, and their wide range of applications, such as in soft robots and actuators, stretched electronic devices, tissue engineering materials, controlled-release drug delivery vehicles, biomedicine materials, food science, and (bio)sensors. In general, there are four core concerns in hydrogel science, including the polymer source, structure fabrication, gel function, and gel applications. According to the logic that the “structure determines function”, it is believed that rational design of structures can effectively regulate the functions and applications of hydrogels. Hence, in the current review, “structure” as the core topic will be highly regarded, and the crosslinking mechanisms and structural diversity of hydrogels are comprehensively summarized. Additionally, hydrogels also show their great application potential in food science. Hence, the current review also pays more attention to the application of hydrogels in food nutrition and health, food engineering and processing, and food safety. It is whished that this review not only serves as a reference for improving the comprehensive understanding of the structural design of hydrogels but also provides a forward-looking idea for hydrogel applications in food science. Graphical abstract Graphical Abstract