The effect of organic matter on ammonium release kinetics and adsorption isotherms of the sediments from different trophic level urban rivers(named TL, HH and TJ) and its mechanism was discussed. The results showed the removal ratio of organic matter of per unit volume of H₂O₂ tended to decrease with volume of H₂O₂ increasing. The content of ammonium in sediments tended to increase significantly as sediment organic matter was removed by H₂O₂. Ammonium adsorption capacity tended to decrease with their organic matter contents decreasing. The equilibrium time of ammonium release was prolonged with the increasing of the organic matter contents in the studied sediment, and the amounts of the ammonium released increased first and then reached equilibrium gradually. Removal of organic matter could increase ammonium release capacity. The main factors affecting ammonium release were analyzed. Organic matter content and ammonium concentration were the key factors on ammonia release from sediments.