In　this　research,　the　numerical　model　of　fresh　self-compacting　concrete　(SCC)　U-box　test　was　established　by　combining　lattice　Boltzmann　method　(LBM)　and　Herschel-Bulkley　(H–B)　model.　The　flow　behavior　of　fresh　SCC　in　U-box　was　studied　and　its　rheological　mechanism　was　analyzed.　The　test　results　showed　that　the　simulation　model　established　based　on　U-box　test　had　high　simulation　accuracy,　and　the　average　error　was　about　7　%.　The　effects　of　rheological　parameters　(power-law　index　n,　consistency　index　k　and　yield　stress　σ0)　on　the　U-box　test　were　explored.　The　numerical　results　demonstrated　that　σ0　was　the　crucial　rheological　parameter　that　determined　the　passing　ability　of　fresh　SCC,　and　its　increase　resulted　in　weaker　passing　ability.　n　and　k　had　less　effect　on　the　passing　ability.　At　the　early　stage　of　U-box　test　(t　0　all　reduced　the　velocity　of　flow　and　the　pressure　exerted　on　the　fresh　SCC,　with　n　bringing　the　most　significant　effect.　The　peak　velocity　and　pressure　of　shear-thinning　(n　=　0.6)　SCC　could　reach　0.74　m/s　and　4200　Pa　at　t　=　0.1　s.　The　peak　velocity　of　shear-thickening　(n　=　1.4)　SCC　was　less　than　half　of　the　former,　and　a　larger　negative　pressure　appeared,　up　to　about　−1600　Pa.　The　speed　of　pulling　up　the　partition　gate　(ug)　only　had　an　effect,　which　gradually　diminished　with　the　increase　of　ug,　on　the　initial　phase　of　U-box　test　(t　©　2022　Elsevier　Ltd