The model of second-order reaction kinetics has been used to stimulate the monochloramine decay in model and distribution system waters by nonlinear fit. Several factors were investigated, including pH, bromide, nitrite concentrations in this system. The results showed that pH value was an important factor on the monochloramine decay rate, especially when pH was below 7.0. Presence of bromide ions had different impact under experimental conditions However, when pH was above 7.60, 0.1 mg/L concentration of bromide affect hardly the decay rate of mononchloramine. The results demonstrated that the second-order kinetic model could fit well the experimental results of monochloramine decay reaction under the conditions of bromide, and nitrite ion. Finally, the work presented here validates and extends this model for use in distribution systems under realistic chloramination conditions.