Biofilms　have　extensive　applications　and　important　roles　in　biological　processes.　This　study　aimed　to　investigate　the　effect　and　mechanism　of　low-concentration　sulfamethoxazole　(SMX)　on　biofilm　development　in　biofilters.　The　effects　of　various　SMX　concentrations　(0,　100　ng/L,　1000　ng/L)　on　microbial　development　were　compared.　Compared　with　the　control　group　without　SMX,　the　start-up　period　of　R2　and　R3　filters　with　SMX　added　was　decreased　by　9　%　and　21　%,　respectively.　Under　antibiotic　stimulation,　reactive　oxygen　species　(ROS)　and　bis(3　＇-5　＇)-cyclic　dimeric　guanosine　monophosphate　(c-di-GMP)　concentrations　increased,　aligning　with　changes　in　extracellular　polymer　content　and　biofilm　formation.　Microbial　community　results　showed　that　the　presence　of　SMX　promoted　the　growth　of　some　manganese-oxidizing　bacteria　(MnOB),　such　as　Massilia,　Pedomicrobium,　Sphingopyxis,　Pseudomonas,　and　Bacillus.　Functional　gene　analysis　further　revealed　higher　expression　levels　of　genes　related　to　c-di-GMP　transformation　in　the　presence　of　SMX.　These　findings　suggest　that　microbial　communities　can　adapt　to　their　environment　by　accelerating　biofilm　formation　at　lower　antibiotic　concentrations.　The　results　of　this　study　provide　new　insights　into　the　impact　of　low-concentration　antibiotics　on　biofilm　development　and　offer　a　crucial　reference　for　biofilter　design　and　optimization.