Abstract: In order to verify the feasibility or reliability of gel-embedded nitrobacteria carriers and to obtain parameters for engineering application，the gel-embedded nitrobacteria carriers was combined with A/O system’activation condition and treatment effect was to be studied under the condition of low temperature． The result indicated that the activation time for the system of activated gel-embedded nitrobacteria carriers was about 10d，no more than 15 d at a low temperature of 13 ℃ to 15 ℃． And under stable operation and load increasing ( increasing to 1. 44 times) stage，the system of gel-embedded nitrobacteria carriers to treat urban sewage can make an average of below 1 mg /L ammonia nitrogen in the effluent and the removal rate of ammonia nitrogen was more than 99% under the sludge concentration of 3 000 ～ 3 500 mg /L and dosing rate of 12%． Furthermore，the treatment effect of gel-embedded nitrobacteria carriers combined with A/O system was better than A/O system under the same conditions．