The rapid development of the Internet of Things and artificial intelligence has driven the need for wearable, portable, and self-powered flexible sensing devices. Triboelectric nanogenerators (TENGs) based on gel materials, which offer excellent conductivity, mechanical tunability, environmental adaptability, and biocompatibility, are emerging as a promising approach for developing new-generation flexible sensors. This review comprehensively summarizes recent advances in gel-based TENGs for flexible sensors, covering their principles, properties, and applications. Gels, categorized into hydrogels, organogels, and aerogels, are three-dimensional network structures with unique properties that make them suitable for flexible TENGs. Hydrogels, with their good flexibility and tunable mechanical properties, are particularly useful for applications requiring frequent deformation and stress changes, such as electronic skin and wearable sensors. Organogels, known for their mechanical flexibility and stability, can maintain good flexibility and stretchability over a wide range of stress and environmental conditions, making them suitable for long-term monitoring of bending motions. Aerogels, with their high porosity and thermal insulation, are ideal for high-temperature and gas sensing applications. The working mechanisms of gel-based TENGs include vertical contact-separation, lateral sliding, single-electrode, and freestanding tribolayer modes. The single-electrode mode, which combines the advantages of single-electrode and gel materials, is particularly suitable for flexible wearable sensors due to its simplicity and direct contact with human skin. To enhance the performance of gel-based TENGs, various strategies have been employed. For hydrogels, improvements in conductivity, mechanical properties, and self-healing capabilities have been achieved through the introduction of conductive fillers, nanofillers, and dynamic chemical and physical bonding. Organogels have been optimized for mechanical toughness, temperature tolerance, and environmental adaptability through the use of sacrificial networks, microphase separation, and solvent replacement. The applications of gel-based TENGs in human motion sensing, tactile sensing, health monitoring, environmental monitoring, and human-machine interaction are highlighted. Despite the progress, challenges remain, including the need for enhanced performance in dynamic mechanical deformations, shape adaptability to irregular surfaces, and operational stability in extreme environments. Future research should focus on developing effective solutions to address these challenges, guiding the development and application of gel-based TENGs in flexible sensing.The rapid development of the Internet of Things and artificial intelligence has driven the need for wearable, portable, and self-powered flexible sensing devices. Triboelectric nanogenerators (TENGs) based on gel materials, which offer excellent conductivity, mechanical tunability, environmental adaptability, and biocompatibility, are emerging as a promising approach for developing new-generation flexible sensors. This review comprehensively summarizes recent advances in gel-based TENGs for flexible sensors, covering their principles, properties, and applications. Gels, categorized into hydrogels, organogels, and aerogels, are three-dimensional network structures with unique properties that make them suitable for flexible TENGs. Hydrogels, with their good flexibility and tunable mechanical properties, are particularly useful for applications requiring frequent deformation and stress changes, such as electronic skin and wearable sensors. Organogels, known for their mechanical flexibility and stability, can maintain good flexibility and stretchability over a wide range of stress and environmental conditions, making them suitable for long-term monitoring of bending motions. Aerogels, with their high porosity and thermal insulation, are ideal for high-temperature and gas sensing applications. The working mechanisms of gel-based TENGs include vertical contact-separation, lateral sliding, single-electrode, and freestanding tribolayer modes. The single-electrode mode, which combines the advantages of single-electrode and gel materials, is particularly suitable for flexible wearable sensors due to its simplicity and direct contact with human skin. To enhance the performance of gel-based TENGs, various strategies have been employed. For hydrogels, improvements in conductivity, mechanical properties, and self-healing capabilities have been achieved through the introduction of conductive fillers, nanofillers, and dynamic chemical and physical bonding. Organogels have been optimized for mechanical toughness, temperature tolerance, and environmental adaptability through the use of sacrificial networks, microphase separation, and solvent replacement. The applications of gel-based TENGs in human motion sensing, tactile sensing, health monitoring, environmental monitoring, and human-machine interaction are highlighted. Despite the progress, challenges remain, including the need for enhanced performance in dynamic mechanical deformations, shape adaptability to irregular surfaces, and operational stability in extreme environments. Future research should focus on developing effective solutions to address these challenges, guiding the development and application of gel-based TENGs in flexible sensing.