To explore the removal route of ammonia nitrogen, a biological purification process operation test for high concentration of iron and manganese associated ammonia nitrogen [Fe(Ⅱ) 9.2-15.1 mg/L, Mn(Ⅱ) 0.6-1.4 mg/L, NH+₄-N 0.9-2.0 mg/L] was carried out at low temperature (5-6 ℃) in a groundwater plant for iron, manganese, and ammonia nitrogen removal. Results show that the filter column had good removal effect of ammonia nitrogen at the initial stage of start-up. The analysis along the process and the adsorption test of mature filter material and backwash sludge show that when the influent ammonia nitrogen was about 1.1 mg/L, the ammonia nitrogen was mainly removed by the iron and manganese oxides in the upper part of the filter layer, and the removal rate by biological action was very small. In order to further explore the biological and adsorption effects of filter column on ammonia nitrogen, gradient was used to adjust the concentration of ammonia nitrogen in influent. With the increase of the influent ammonia nitrogen concentration, the ammonia nitrogen removal by biological action increased. Under the condition of influent iron and manganese concentration, the ammonia nitrogen removal by iron and manganese oxides adsorption was about 1 mg/L in the upper 20 cm range of the filter.