Arsenic　(As)-contaminated　soil　poses　great　health　risk　to　human　mostly　through　inadvertent　oral　exposure.　We　investigated　CaAl-layered　double　hydroxide　(CaAl-LDH),　a　promising　immobilising　agent,　for　the　remediation　of　As-contaminated　Chinese　soils.　The　effects　on　specific　soil　properties　and　As　fractionation　were　analyzed,　and　changes　in　the　health　risk　of　soil　As　were　accurately　assessed　by　means　of　advanced　in　vivo　mice　model　and　in　vitro　PBET-SHIME　model.　Results　showed　that　the　application　of　CaAl-LDH　significantly　increased　soil　pH　and　concentration　of　Fe　and　Al　oxides,　and　effectively　converted　active　As　fractions　into　the　most　stable　residual　fraction,　guaranteeing　long-term　remediation　stability.　Based　on　in　vivo　test,　As　relative　bioavailability　was　significantly　reduced　by　37.75%.　Based　on　in　vitro　test,　As　bioaccessibility　in　small　intestinal　and　colon　phases　was　significantly　reduced　by　25.65%　and　28.57%,　respectively.　Furthermore,　As　metabolism　(reduction　and　methylation)　by　the　gut　microbiota　inhabiting　colon　was　clearly　observed.　After　immobilisation　with　CaAl-LDH,　the　concentration　of　bioaccessible　As(V)　in　the　colon　fluid　was　significantly　reduced　by　61.91%,　and　organic　As　(least　toxic　MMA(V)　and　DMA(V))　became　the　main　species,　which　further　reduced　the　health　risk　of　soil　As.　In　summary,　CaAl-LDH　proved　to　be　a　feasible　option　for　immobilisation　remediation　of　As　-contaminated　soils,　and　considerable　progress　was　made　in　relevant　health　risk　assessment.