The ammonia-nitrogen wastewater treatment process with internal circulation three-phase bio-fluidized bed has big inertia of 1800s and uncertainties. It is a kind of object with complex biological and chemical action and hard to obtain nice characteristics. Take the brief mathematical model to represent the process, study Active-disturbance Rejection Control scheme by simulation to keep ammonia-nitrogen concentration of water out stable and meet the boundary, and save energy by avoiding over-aeration when the outside or internal disturbance exists. Set the output limiter of ADRC and tune parameters of it. It turns out that the system has zero static error and zero overshoot with settling time less than or equal to 2000s when the reference and disturbance input are step. It also shows ADRC has stronger robustness. The performance could overcome the inaccuracy and uncertainty of the object model, thus one-order ADRC is applicable to the ammonia-nitrogen wastewater treatment process with ITFB.