Tunnels　crossing　inactive　faults　may　experience　large　differential　deformations　along　their　lengths　during　earthquakes,　resulting　in　damage.　Faults　always　have　inferior　material　properties　for　historical　geological　rea-sons.　Grouting　is　an　auxiliary　construction　measure　in　fault-crossing　tunnels　and　has　the　potential　to　be　an　economical　and　effective　aseismic　measure.　However,　the　feasibility　and　seismic　mitigation　mechanisms　of　grouting　in　fault-crossing　tunnels　have　not　been　sufficiently　studied.　In　this　study,　large-scale　shaking　table　tests　were　conducted　to　verify　the　aseismic　effect　of　grouting　in　a　tunnel　crossing　an　inactive　fault　and　to　explore　the　seismic　mitigation　mechanism　behind　it.　On　this　basis,　verified　numerical　models　were　developed　to　determine　the　optimized　design　parameters.　The　test　results　indicate　that　grouting　reduces　the　acceleration　response　of　the　tunnel　within　the　fault　and　reduces　the　differences　in　the　acceleration　responses　in　the　longitudinal　direction　of　the　tunnel　induced　by　the　fault.　As　grouting　increases　the　shear　strength　and　stiffness　of　the　strata　around　the　tunnel　within　the　fault,　the　strain　of　the　tunnel　invert　is　effectively　reduced　by　over　80%,　and　the　potential　damage　of　the　invert　uplift　is　reduced　simultaneously.　Meanwhile,　grouting　effectively　reduces　the　diameter　deformation　of　the　tunnel　within　the　fault　and　reduces　the　differences　in　tunnel　deformation　in　different　areas　of　the　fault　site.　By　reducing　the　resonance　caused　by　the　frequency　components　of　the　input　seismic　wave　that　is　close　to　the　natural　frequency　of　the　strata,　which　contributes　most　to　the　tunnel　response,　grouting　effectively　reduces　the　seismic　responses　of　the　fault-crossing　tunnels.　Increasing　the　stiffness　of　the　grouting　zone　is　an　effective　approach　to　improve　its　seismic　mitigation　performance.　In　the　example　of　this　study,　adjusting　the　relative　stiffness　ratio　to　approximately　100　between　the　grouting　zone　and　the　fault　resulted　in　a　favorable　condition　for　aseismic　effects,　which　could　be　deemed　to　be　a　suitable　parameter　for　grouting.　The　above　results　can　provide　a　reference　for　the　seismic　design　of　mountain　tunnels　crossing　inactive　faults.