Disclosed are a surface plasmon resonance (SPR) fiber grating biosensor and a method for detecting viruses. The surface plasmon resonance (SPR) fiber grating biosensor includes an optical broadband source (BBS), an optical specturm analyzer (OSA), a polarization controller, and a linear polirizer. The optical broadband source (BBS) from an erbium-doped fiber amolifier (EDFA) is configured to illuminate an optical beam of a tilted fiber brag grating (TFBG). The TFGB is coated with a gold (Au) layer and a monoclonal antibody (Mab) is immobilized on the gold layer via an anime interlayer coupling. The optical spectrum analyzer (OSA) is configured to analyze the optical beam to obtain a transmission spectrum. The polarization controller is configured to adjust a polarization state of the optical beam. The linear polarizer is configured to linearly polarize the input optical beam.