The treatment characteristics of a pilot scale fluidized bed reactor with embedded nitrobacteria was investigated to rapidly remove ammonia from Wenruitang River. Results showed that 45.50% of the ammonia nitrogen in the Wenruitang River was removed by the fluidized bed reactor with the average influent ammonia nitrogen concentration of 6.15 mg/L. The main product of the nitrification process was nitrate nitrogen. CODMn could also be removed during the treatment process. Harmful ammonia nitrogen in urban rivers could be rapidly be removed by the fluidized bed reactor with embedded nitrobacteria. This could be applied in the treatment of urban river water.