Glass　Fiber-Reinforced　Polymer　(GFRP)　finds　extensive　applications　in　the　high-end　equipment　manufacturing　industry　owing　to　its　advantages　of　light　weight,　high　strength,　and　corrosion　resistance.　Since　the　residual　stress　in　GFRP　builds　up　during　the　curing　process　and　affect　its　mechanical　properties　and　service　life,　the　characterization　of　the　residual　stress　in　GFRP　is　crucial.　In　this　study,　we　establish　a　theoretical　model　based　on　the　anisotropic　stress-optics　law　for　the　orthorhombic　crystalline　system　to　describe　the　terahertz-elasticity　of　GFRP　and　calibrate　the　stress　optical　coefficients　of　GFRP.　First,　the　residual　stress　in　GFRP　at　different　curing　temperatures　are　measured　by　fiber　Bragg　grating　sensors.　Then,　the　refractive　index　of　GFRP　with　different　residual　stress　are　obtained　based　on　transmission-type　THz-TDS.　Finally,　based　on　the　proposed　photoelastic　model　of　GFRP,　the　stress　optical　coefficients　of　GFRP　are　measured　by　combining　the　measurement　results　of　residual　stress　and　refractive　index.　The　experimental　results　show　that　the　refractive　index　of　GFRP　decreases　with　the　increase　of　residual　stress;　the　stress　optical　coefficients　of　GFRP　are　determined　as　q11　=　-5.612　x　10-9　Pa-　1,　q12　=　-2.548　x　10-9　Pa-　1,　q21　=　-1.305　x　10-　8　Pa-　1,　q22　=　-1.408　x　10-9　Pa-　1.　The　modeling　of　terahertz　photoelasticity　in　GFRP　and　the　determination　of　stress　optical　coefficients　provide　a　basis　for　characterizing　residual　stress　in　GFRP　by　THz-TDS.