Hydrogels are a class of hydrophilic materials made of polymers cross-linked by physical entanglement or covalent bonds, capable of absorbing large amounts of water while remaining insoluble. Due to their excellent biocompatibility, tunable mechanical properties, and responsiveness, hydrogels hold significant potential for applications in biomedicine, agriculture, environmental protection, and industry. Despite this promise, current hydrogels still face several challenges in practical applications. This paper examines the development trends of hydrogels by reviewing their classification, preparation methods, and primary existing and potential applications in biomedicine, environmental protection, and industry, aiming to provide a reference for advancing hydrogel applications. This paper highlights that by continuously optimizing and innovating hydrogel materials and preparation processes, more novel and efficient applications can be achieved, fostering scientific and technological progress and social development.