Mixing　material　such　as　fibers　into　concrete　is　an　effective　method　to　change　the　brittle　behavior　of　concrete.　To　reduce　the　internal　defects　of　concrete　and　improve　the　mechanical　performance　and　crack　resistance　of　concrete,　this　study　proposed　the　design　concept　of　multiscale　modified　concrete.　To　further　investigate　the　feasibility　of　the　design　concept,　the　two-stage　test　method　is　adopted　to　study　the　performance　of　multiscale　modified　concrete.　First,　carbon　nanotubes　(CNT)　and　CaCO3　whiskers　were　mixed　into　concrete,　and　the　optimum　contents　of　CNT　and　CaCO3　whiskers　were　determined　by　uniaxial　compression　test.　Subsequently,　based　on　the　optimum　contents　of　CNT　and　CaCO3　whiskers,　polyvinyl　alcohol　fibers　(PVAF),　steel　fibers　(SF),　and　rubber　particles　(RP)　were　further　mixed　into　concrete,　and　the　uniaxial　compression　test　and　scanning　electron　microscopy　(SEM)　test　were　completed.　From　the　test　results,　the　influence　of　materials　contents　on　the　mechanical　performance　of　concrete　was　analyzed,　an　accurate　and　reasonable　compressive　stress-strain　model　was　established,　and　the　comprehensive　toughness　evaluation　index　of　concrete　considering　the　multiple　factors　influence　was　presented.　The　comprehensive　toughness　evaluation　results　show　that　the　multiscale　modified　concrete　has　outstanding　compressive　strength　and　toughness　when　the　contents　of　CNT,　CaCO3　whiskers,　PVAF,　SF,　and　RP　are　0.6%,　6.0%,　0.075%,　1.0%,　and　0%,　respectively.　The　SEM　results　revealed　that　adding　materials　of　various　sizes　into　concrete　can　hinder　the　growth　of　cracks　and　improve　the　cracking　pattern　of　concrete.　©　2023　American　Society　of　Civil　Engineers.