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In recent years, hydrogels have attracted extensive attention due to their unique properties. More and more studies have added new functions to hydrogels through modification, but the modified hydrogels only show unique properties in a specific aspect, which limits the application of hydrogels. Therefore, how to endow hydrogels with two or more functions at the same time has become a research hotspot. In this study, polyacrylamide and chitosan quaternary ammonium salt were used as the matrix of the hydrogel. The surface of magnetic ferric oxide nanoparticles (Fe 3 O 4 NPs) was modified by tannic acid (TA). TA and Fe 3 O 4 NPs were connected by coordination bonds to improve the surface properties of Fe 3 O 4 NPs. Then aniline molecules were coated on the surface of Fe 3 O 4 -TA NPs by the electrostatic attraction through in-situ chemical polymerization under the action of sulfuric acid doping to obtain composite Fe 3 O 4 NPs with electromagnetic dual functions. The electromagnetic bifunctional hydrogel was prepared by introducing the composite Fe 3 O 4 NPs into the hydrogel through physical doping. The results showed that the hydrogel had excellent mechanical properties (the tensile strength was 113.3 kPa, the elongation was 1070%). Due to the existence of polyaniline, the hydrogel showed outstanding electrical properties (the conductivity was up to 24.3 mS/cm and the gauge factor was up to 9.43). In addition, Fe 3 O 4 NPs gave the hydrogel good magnetism, and the hydrogel underwent a certain deformation in the switching magnetic field, which further expanded the application field of the hydrogel. Synthesis process and structure of electromagnetic bifunctional hydrogel. [Display omitted] • Tannic acid used as coupling agent to connect Fe 3 O 4 with polyaniline. • Fe 3 O 4 composite particles act as physical cross-linking points in the hydrogel. • Hydrogels have electromagnetic dual functions and high sensing sensitivity. [ABSTRACT FROM AUTHOR]