In　order　to　find　the　influence　of　alkalinity　on　the　formation,　breakup　and　regrowth　of　flocs,　photometric　dispersion　analyzer　(model　PDA2000)　is　applied　to　investigate　flocculation　index　(FI　index)　of　flocs　formed　by　kaolin　suspension　with　aluminum.　The　strength　factor　and　the　regrowth　factor　are　used　to　evaluate　the　flocs　strength　and　the　regrowth　of　broken　flocs.　The　results　shows　that　the　formation,　breakup　and　regrowth　process　of　flocs　are　affected　by　alkalinity　to　a　great　extent,　and　the　floc　particle　diameters　reduce　with　the　increase　of　alkalinity.　The　flocs　strength　is　determined　by　both　coagulant　dosage　and　alkalinity.　The　flocs　strength　becomes　higher,　when　higher　alkalinity　and　more　coagulant　dosage　are　added.　The　regrowth　degree　of　flocs　formed　mainly　with　charge　neutrality　action　is　approached　about　100%　in　the　first　breakup　process　under　low　alkalinity.　For　the　flocs　resulted　mainly　from　sweep　coagulation　action,　the　FI　index　is　reduced　with　more　than　10%　degree　each　time　from　the　second　breakup　process　and　the　flocs　strength　is　reduced　remarkably　without　relation　to　alkalinity.