To investigate catalytic oxidation of ammonium from groundwater by a co-oxide filter film coating on quartz sands, a pilot-scale filter which has been operated for about 4years was used, and varying inlet ammonia loads and the filter was operated under inlet water only containing ammonia for long term. Results showed that in the experimental conditions of the concentration of ammonia nitrogen was 0.8~1.3mg/L, the temperature of raw water was 20~23℃, and the flow rate was 7m/h, the performance of catalytic oxidation of ammonium of the co-oxide filter film remained stable and high-efficient for a long time. The maximum ammonium removal capacity of the filter was determined to be 22.2g NH₄⁺-N/(m³·h) with ammonium removal rate(ARR) determined by the ammonium loading rate(ALR) if the dissolved oxygen(DO) was enough. The maximum concentration of ammonia was limited by DO. When the DO in influent was not enough, flow rates had significant influence on consumption of dissolved oxygen along the filter layer.