Chloramine under UV photolysis could not only produce the widely known hydroxyl radical (HO^•) and reactive chlorine species (RCS; e.g., ClO^•, Cl₂^•− and Cl^•), but also produce reactive nitrogen species (RNS; e.g., ^•NH₂, ^•NO and ^•NO₂). In this study, the kinetic mechanisms, degradation products, N-Nitrosodimethylamine (NDMA) formation of RAN in the UV/chloramine process were investigated. The RAN degradation by UV/chloramine process well fitted the pseudo-first order kinetic model and exhibited a synergistic improvement compared with UV photolysis and chloramination alone. HO^• is the predominant radical that contributes to RAN degradation in the range of solution pH from 6.0 to 8.0 (from 43.4% to 56.3%), and RNS was confirmed to contribute to RAN degradation through experiments. As the concentrations of HCO₃⁻, Cl⁻ and NO₃⁻ (0 ~ 4 mM), chloramine dosage (200 ~ 300 μM), solution pH (6.0 ~ 8.0) and natural organic matter (0 ~ 4 mg-C L^-1) increased, the RAN degradation in UV/chloramine process was inhibited. Besides, the second-order rate constant between CO₃^•- and RAN was determined to be 8.05 × 10⁶ M⁻¹ s⁻¹ in this study. A possible pathway and reaction schemes of RAN degradation by UV/chloramine process were proposed, which could also be used to explain the role of RNS in the NDMA formation. During the treatment of RAN by chloramination alone and UV/chloramine, NDMA has a better formation potential at both pH = 7.0 and pH = 8.0. Although RNS were responsible for NDMA formation during the RAN degradation by UV/chloramine process, UV photolysis and extending the photolysis time from 5 to 10 min could degrade NDMA and its precursors. Overall, the high yield and toxicity of NDMA should be concerned when choosing the UV/chloramine process.