Conductive hydrogels are a new type of functional polymer materials with a soft and wet three-dimensional structure, featuring high water content, good biocompatibility and excellent electrical conductivity. The hydrogel based flexible electronics overcome the limitations of traditional rigid components and achieve direct, continuous and precise monitoring. Hydrogel sensors are involved in multiple fields such as electrophysiology, human motion, machine learning and respiratory detection in the construction of flexible wearable systems. However, hydrogel flexible electronics face issues such as low sensitivity, large detection limit and poor stability. In the future, high-sensitivity, long-stable, porous and multi-stimuli-responsive hydrogel flexible sensors should be developed, and machine learning technology should be utilized to achieve intelligent perception.