The　demand　and　application　of　buried　structures　have　greatly　increased　recently.　With　space　partially　or　fully　confined,　the　safety　of　buried　structures　subjected　to　internal　hazards　such　as　explosions　is　a　major　concern.　In　the　present　study,　confined　blast　mitigation　effectiveness　of　buried　steel　boxes　with　foam　concrete　is　experimentally　and　numerically　investigated.　Tests　with　and　without　foam　concrete　layer　applied　to　buried　steel　boxes　were　conducted,　with　which　numerical　models　were　established　and　validated.　Factors　influencing　the　mitigation　effectiveness,　such　as　the　crushing　strength　and　thickness　of　foam　concrete,　loading　density,　are　examined　and　discussed　in　detail.　It　is　found　that　for　typical　loading　density,　applying　foam　concrete　layer　effectively　mitigates　confined　blast.　The　protection　effectiveness　in　terms　of　steel　box　deformation　improves　with　increasing　foam　concrete　crushing　strength　and　thickness.　Ineffective　or　even　negative　mitigation　may　occur　if　the　foam　concrete　layer　is　insufficient,　which　should　be　identified　and　avoided.