COVID-19　has　threatened　human　lives.　However,　the　efficiency　of　combined　interventions　on　COVID-19　has　not　been　accurately　analyzed.　In　this　study,　an　improved　SEIR　model　considering　both　real　human　indoor　close　contact　behaviors　and　personal　susceptibility　to　COVID-19　was　established.　Taking　Hong　Kong　as　an　example,　a　quantitative　efficiency　assessment　of　combined　interventions　(i.e.　close　contact　reduction,　vaccination,　mask-wearing,　school　closures,　workplace　closures,　and　body　temperature　screening　in　public　places)　was　carried　out.　The　results　showed　that　the　infection　risk　of　COVID-19　of　students,　workers,　and　non-workers/students　were　3.1%,　8.7%,　and　13.6%,　respectively.　The　basic　reproduction　number　R0　was　equal　to　1　when　the　close　contact　reduction　rate　was　59.9%　or　the　vaccination　rate　reached　89.5%.　The　results　could　provide　scientific　support　for　interventions　on　COVID-19　prevention　and　control.　©　2022　17th　International　Conference　on　Indoor　Air　Quality　and　Climate,　INDOOR　AIR　2022.　All　rights　reserved.