The　purpose　of　present　study　is　to　investigate　the　effect　of　global　stiffness　on　the　force　response　of　thin　GFRP　reinforced　concrete　slabs　simply　supported　by　steel　beams　under　drop-weight　impact.　Considering　the　strain　rate　effect　of　GFRP　bars　and　concrete　materials,　a　numerical　model　of　GFRP-RC　slabs　was　established　and　verified.　The　dynamic　equilibrium　relationship　of　the　impact　force,　reaction　force　and　inertial　force　was　analyzed　and　intuitively　explained　from　the　velocity　and　displacement.　Meanwhile,　the　effects　of　the　global　stiffness　by　varying　the　slab　length,　slab　thickness　and　reinforcement　ratio　on　the　acceleration　distribution,　characteristic　value　of　impact　force　and　reaction　force,　failure　pattern,　displacement　distribution　and　energy　dissipation　were　evaluated　in　more　detail.　Eventually,　the　semi-empirical　formulas　considering　key　parameters　were　proposed　to　predict　the　reaction　force　time　history　of　simply-supported　RC/FRP-RC　slabs　under　drop　hammer　impact.　The　results　show　that　the　effect　of　the　slab　stiffness　by　varying　the　slab　length　and　thickness　on　the　reaction　force　is　significant,　while　the　influence　of　reinforcement　ratio　is　not　obvious.　The　effect　of　global　stiffness　of　the　slab　on　the　plateau　value　of　the　reaction　force　is　similar　to　that　on　the　plateau　value　of　the　impact　force.　The　effect　of　the　slab　stiffness　by　varying　the　slab　thickness　and　reinforcement　ratio　on　the　displacement　is　obvious,　while　varying　the　slab　length　hardly　affects　the　deformation.　The　fitting　equation　considering　key　parameters　can　predict　the　simplified　reaction　force　time　history　of　simply-supported　RC/FRP-RC　slabs　under　impact　loading.　However,　more　experimental　validation　and　extensive　parametric　studies　are　needed　to　improve　their　accuracy　and　applicability.　©　2023　Elsevier　Ltd