In　rural　areas　of　China,　septic　tanks　are　still　the　only　treatment　facilities　before　the　direct　discharge　of　domestic　sewage　in　many　families.　However,　the　effluent　quality　of　the　traditional　three-chamber　septic　tanks　is　poor,　resulting　in　the　pollution　of　rural　water　environment.　It　will　be　one　of　the　effective　ways　to　solve　the　pollution　problem　through　the　modification　of　traditional　three-chamber　septic　tank.　Thus,　the　structure　and　function　optimal　design　of　traditional　three-chamber　septic　tank　was　performed.　In　the　first　chamber,　a　pretreatment　aeration　tank　and　a　pretreatment　sedimentation　tank　were　separated　by　a　overflow　plate.　In　the　second　chamber,　the　anaerobic　fermentation　tank　was　retained.　And　the　third　chamber　was　separated　into　a　biological　contact　oxidation　tank　and　a　secondary　sedimentation　tank　by　a　overflow　plate.　The　results　showed　that　after　stable　operation,　the　removal　rates　of　COD,　NH+4-N,　TP　and　SS　by　the　reactor　could　reach　83.51%~88.56%,　66.82%~74.17%,　77.47%~81.12%,　82.26%~88.57%,　respectively,　which　had　a　significant　improvement　compared　with　the　traditional　septic　tank.　The　modified　rural　three-chamber　septic　tank　realizes　the　on-site　treatment　of　decentralized　sewage　in　rural　areas,　and　its　economy　and　maintenance　convenience　can　meet　the　requirements　of　rural　sewage　treatment　facilities,　this　provides　a　reference　for　the　transformation　and　construction　of　rural　three-chamber　septic　tank.　©　2020,　Science　Press.　All　right　reserved.