The　dynamic　deformation　and　stress　characteristics　of　subgrade　under　two　impact　loading　routes　with　different　compact　times　are　analyzed　based　on　three　dimensional　elastoplastic　dynamic　FEM.　The　results　indicate　that　the　three　dimensional　compressive　stresses　exist　in　the　affected　scope　of　subgrade　underneath　the　slab.　Vertical　deformation　of　subgrade　under　slab　corner　is　maximum;　and　vertical　deformation　of　subgrade　under　slab　corner　is　minimum.　By　comparison　vertical　deformation　of　subgrade,　vertical　deformation　of　subgrade　is　generally　lower.　Vertical　deformation　of　subgrade　increases　with　distance　far　away　from　impact　point.　And　vertical　deformation　of　subgrade　exists　obviously　residual　deformation,　wave　and　hysteresis　phenomenon.　Vertical　deformation　of　subgrade　increases　with　increasing　of　compact　times;　and　there　exists　plastic　zone　after　the　third　compact　time.　Soil　pressure　increases　with　increasing　of　compact　times;　but　increasing　tendency　tends　to　be　stable.　The　range　of　increasing　soil　pressure　is　limited　to　certain　depth　of　subgrade.