A　grading　cross　bio-trickling　filter　was　designed　for　H2S　removal.　Mixed　microorganisms　domesticated　from　the　former　experiment　were　immobilized　to　start　up　the　trickling　filter.　Removal　performances　during　starting　up　period　and　different　loadings　were　investigated.　Results　showed　that　the　immobilization　of　the　trickling　filter　was　completed　within　3　d.　The　removal　efficiency　was　higher　than　99%　when　the　inlet　concentration　was　in　the　range　of　110　mg·m-3　to　230　mg·m-3　(EBRT　30　s).　At　low　inlet　loadings,　the　front　part　of　the　trickling　filter　played　a　major　role　in　H2S　degradation,　accounting　for　about　85%.　Microbial　diversity　and　population　of　the　front　part　were　superior　to　the　tail　one.　At　higher　loadings,　microbial　diversity　and　population　of　the　tail　part　increased　significantly,　from　4.5×107　cells·g-1　to　5.17×108　cells·g-1,　and　the　elimination　capacity　was　also　improved,　from　0.04　g·h-1　to　0.67　g·h-1.　Rod-shaped　bacteria　were　the　dominant　microorganisms　on　the　surface　of　ceramics　in　the　steady　state　as　observed　by　SEM.The　surfaces　of　ceramics　were　covered　by　a　lot　of　microbial　metabolites　at　high　loadings.　Analysis　of　the　metabolites　indicated　that　the　majority　of　H2S　was　oxidized　to　sulfur　and　only　a　small　portion　was　converted　to　sulfate.