Effects of various pH and COD on bacteriagrowth and bactericidal performance while Niukouyureservoir wastewater is being reused as cooling water have been studied.The results show that pH<7 facilitatesiron bacteriagrowth,and has no effects to the growth of bacteriaand sulfate-reducingbacteria.Different pH values have no effects to dichloroisocy anuricacid so diumsaltand dode cyldimethyl benzy lammonium chloride'sbactericidal performance.Is othiazolinisn'tsuitable for bactericidal performance while Niukouyuwastewater is being reused.High COD could facilitate bacteria growth,andalso promote biocides bactericidal performance.