Abstract: The effect of ferrous ions dosage on the anaerobic ammonia was investigated. The excitation-emission matrix (EEM) fluorescence spectroscopy combined with parallel factor analysis (PARAFAC) method was used to decompose the EEM fluorescence components in the effluent samples. The relationship between the added Fe(Ⅱ) and the effluent quality of the reactor was explored. The results showed that with the increase of ferrous ions concentration from 1.84 mg/L to 5.00 mg/L, the removal rates of N ${\mathrm{H}}_4^{+}$ -N and N ${\mathrm{O}}_2^{-}$ -N increased gradually, indicating that increasing the influent ferrous ions concentration could increase the utilization rate of substrate by microorganisms. The proportion of anammox bacteria increased significantly with the increase of ferrous ions dosage; protein-like substances and fulvic acid-like substances were the main fluorophores in the effluent of anammox reactor. With the increase of ferrous ions dosage, the protein-like fluorescence of the effluents increased significantly, which implicated that the dosage of ferrous ions would promote the growth of anammox bacteria under certain conditions. Therefore, EEM fluorescence spectroscopy could reflect the effect of ferrous ions on the performance of anaerobic ammonia oxidation, which then implicate the actual operation of the reactor.