<p>African swine fever virus (ASFV) is a highly infectious and pathogenic DNA virus with a mortality rate of nearly 100%. Here, we developed a flexible biosensor based on a AgNWs/hydrogel/PS(polystyrene)/Fe₃O₄ composite film for the detection of ASFV P72 protein gene fragments. A large number of carboxyl groups in the hydrogel provide modification sites for capture probes (cp) simplifying the preparation process of the biosensor. Combined with the excellent magnetic properties of Fe₃O₄, the excellent electrical conductivity of silver nanowires (AgNWs) and the unique optical properties of two-dimensional photonic crystals (2DPC), the flexible biosensor can convert biological signals into optical signals and electrical signals, and the micro-deformation of the film can be verified by simple optical methods. In order to improve the sensitivity, we introduce Fe₃O₄ and apply an external magnetic field to amplify the thin film micro-deformation. The concentration of P72 protein gene fragment and the relative change rate of resistance showed a good linear relationship, and the linear equation is <i>y</i> = − 0.00126x − 0.31729; the detection limit (LOD) is as low as 0.208 μM. The composite film was used to detect real serum samples, and the recovery of the composite film fluctuated in the range 91.89 to 103.19%, indicating that the composite film has practical application potential in clinical detection of ASFV. In addition, the biosensor also shows good biocompatibility, stability, and specificity.</p> Graphical Abstract <p></p>