Formation and decay of different forms of chloramines were analyzed in stainless steel loop. The experimental results show that under the Cl/N ratio of 1~12, the formation of free chlorine, monochloramine and total chlorine in different water qualitity follows the ranking of deionized water> bulk water > stainless steel loop; the formation of dichloramine in stainless steel loop is much higher than that in deionized water and bulk water, at Cl/N ratio of 10, it accounts for more than 90% of the total chlorine. Under different Cl/N ratio, dichloramine first increases and then decreases with time and other forms of chloramines continuously decrease with the reaction time. The decay rate of monochloramine under different Cl/N ratio follows as: 6∶1 > 3∶1 > 4∶1 > 5∶1, the concentration of dichloramine has no obvious correlation with Cl/N ratio.