A large quantity of microorganisms are reproduced in circulating water systems. Thus a large quantity of sludge is formed and the sludge lowers the cooling efficiency of the cooling tower. If the sludge deposits in the heat exchanger, the heat exchanging efficiency will decline quickly. The sludge which deposits on the metal surface will result in serious corrosion under the scale. And it will also make the scale and corrosion inhibitors ineffective. Based on an applied effect comparision of several oxidizing bactericides which have been used in the ethylene circulating water systems in Xinjiang Dushanzi in order to control microorganisms, reasonable choice of bactericides is put forward.