Abstract: The control action of synergistic pretreatment of permanganate and chlorine on trihalomethane (THMs) formation is discussed by gas chromatography with laboratory water samples. This article observed the effects of the dosage of permanganate and chlorine on THMs, and also compared the synergistic effects with those of chlorine disinfection only. The results show that chlorine dosage is the main factor in the synergistic disinfection process of permanganate and chlorine. The synergistic disinfection process of permanganate and chlorine may reduce the amount and form of THMs significantly with the increase of disinfectant dosage, by comparision with chlorine disinfection at the same total disinfectant dosage.