A　horizontal　biotrickling　filter　(HBTF)　was　designed　to　understand　the　toluene　removal　process　and　microbial　community　structures.　The　start-up　time　of　the　HBTF,　immobilized　by　the　dominant　fungi　was　only　about　6　days　and　the　toluene　removal　efficiency　was　found　to　be　more　than　95%　when　the　inlet　toluene　concentration　remained　at　around　1560.0　mg/m3.　In　the　stable　operation　stage　of　the　HBTF,　based　on　not　greatly　reducing　the　removal　efficiency,　a　simple　and　convenient　periodic　commutation　was　adopted　to　reduce　the　pressure　drop　(oP)　and　regulate　the　distribution　of　microorganisms　in　the　packing　area　of　the　HBTF.　The　oP　decreased　from　about　90　Pa　to　10　Pa　after　the　commutation,　which　indicated　its　feasibility.　The　performance　of　the　HBTF　was　improved　by　changing　the　inlet　direction　of　waste　gas　flow.　When　the　inlet　concentration　of　toluene　was　about　640　mg/m3,　the　removal　efficiency　was　nearly　70.0%　before　commutation　and　it　remained　95.0-98.0%　after　commutation.　Microbial　abundance　and　diversity　analysis　showed　that　the　corresponding　Shannon-Weiner　index　was　2.73　and　1.84,　respectively.　The　front　section　of　the　HBTF,　which　was　exposed　to　toluene　earlier,　consistently　exhibited　higher　microbial　diversity　than　that　in　the　back　section.　Following　commutation,　microbial　diversity　decreased　in　both　the　front　and　back　sections,　with　a　maximum　decline　of　around　50%.　The　main　fungi　treating　toluene　were　Aplanochytrium,　Boletellus,　and　Exophiala.