The　present　study　was　directed　towards　the　feasibility　and　long-term　operation　efficiency　of　the　purification　of　groundwater　with　low　concentration　of　As(III),　using　iron-based　adsorbent　which　was　in-situ　formed　in　the　filtration　process　by　dosing　ferrous　sulfate,　without　pre-oxidation　technique.　Several　experiments　were　conducted　to　analyze　the　optimal　dosage　ratio　of　the　Fe　and　As,　and　the　effect　of　filtration　rate　and　the　arsenic　removal　mechanism　in　the　filtration　process.　The　results　showed　that　with　the　influent　As　(III)　concentrations　of　50　and　100　μg/L　respectively　for　the　filter　column　R1　and　R2,　and　the　filtration　rate　of　5　m/h,　the　optimal　ferrous　sulfate　dosage　was　1.2　and　2　mg/L　respectively,　and　the　optimal　dosage　ratio　of　Fe　and　As　was　about　201.　The　filter　column　R3　was　adopted　for　advanced　research,　with　the　influent　As　(III)　concentration　of　50-70　μg/L　and　the　total　Fe　concentration　of　about　2　mg/L.　The　As(III)　removal　space　in　the　filter　column　descended　continuously　with　the　increasing　of　filtration　rate,　and　the　removal　process　mainly　occured　in　the　upper　60　cm　filter　layer.　Meanwhile,　the　Fe　removal　space　basically　remained　unchanged:　the　removal　concentration　was　both　about　1　mg/L　for　the　filter　layer　of　0-20　cm　and　20-80　cm　respectively.　In　the　increase　of　the　the　filtration　rate　from　3　m/h　to　10　m/h,　the　maximum　filtration　rate　of　the　filter　column　was　confirmed　to　be　10　m/h,　and　the　backwashing　period　decreased　slightly(remaining　within　72　h).　Intermediate　products　might　be　generated　in　the　autocatalytic　oxidation　process　of　ferrous　ion,　which　were　of　great　benefit　to　the　oxidation　of　As　(III).　The　r-FeOOH　coated　on　the　filter　media　surface　and　the　Fe(OH)3　formed　in　the　filter　media　pore　could　provide　sufficient　sites　for　arsenic　adsorption.　©　2018,　Editorial　Board　of　Journal　of　Harbin　Institute　of　Technology.　All　right　reserved.