Abstract: The dynamic mechanical properties of steel-fiber reinforced ultra high strength concrete with different fiber volume fractions were studied by the split Hopkinson press bar testing method under impact compression with different strain rates.The experimental results show that the steel-fiber reinforced ultra high strength concrete is sensitive to strain rate.The relations between the mechanical properties of steel-fiber reinforced ultra high strength concrete and strain rates are examined.The threshold value of strain rate beyond which the strength,ductility and elastic modulus of steel fiber reinforced ultra high strength concrete is remarkably increased with the increase of the fiber volume fractions.The experiment also demonstrates that adding steel fibers into the ultra high strength concrete matrix has significant effects on the failure pattern of the concrete specimen.Under high strain rate,steel fiber reinforced ultra high strength concrete specimen developed cracks but the overall shape of the specimen remained virtually unaltered,however,under the same strain rate,the ultra high strength concrete matrix specimen without steel fibers were almost smashed into small pieces.