Coagulation　process　is　highly　influenced　by　solution　pH,　floc　breakage,　and　coagulant　aid.　In　this　work,　two-stage　addition　of　alum-based　coagulants,　polyaluminum　chloride　(PACl)　and　aluminum　sulfate　(Al-2(SO4)(3)),　was　compared　to　their　one-stage　addition　with　the　same　total　dosage.　The　dose　ratio　of　primary　and　secondary　addition　was　optimised.　The　effects　of　solution　pH,　floc　breakage　and　dosing　timing　of　coagulant　aid　of　non-ionic　polyacrylamide　(NPAM)　on　coagulation　efficiency　and　floc　property　were　investigated.　The　results　showed　that　two-stage　addition　of　PACl　showed　less　sensitivity　with　the　variation　of　pH.　Compared　to　PACl,　two-stage　addition　of　Al-2(SO4)(3)　was　more　sensitive　to　the　solution　pH,　especially　when　the　pH　ranged　from　7　to　10.　For　all　cases,　the　presence　of　floc　breakage　improved　the　removal　of　colloidal　particles.　The　coagulation　mechanism　of　primary　coagulant　was　charge　neutralisation,　while　other　mechanism　was　involved　with　the　secondary　addition　of　coagulant.　Compared　to　one-stage　addition,　the　settling　performance　of　aggregates　and　particulates　removal　in　two-stage　addition　was　more　effective　with　the　variation　of　dosage　or　dosing　timing　of　NPAM.　The　present　work　provides　detailed　operating　parameters　for　this　coagulation　strategy.