The operation and control strategy has been investigated by using a wastewater treatment process simulator which include IAWQ Activated Sludge Model No. 2. The purpose of simulation is to stabilize the biological nitrogen and phosphorus removal process, especially paying attention to the relationship between a load of organic substrate and the efficiency of phosphorus removal.The organic substrate concentration was observed at some points of sewer, and the simulation used these measured values as a influent condition. The phosphorus removal efficiency was estimated to be 91.8% on the condition of the sewage at upper part of sewer. But it was estimated to be 49.9% on the condition of the sewage at an inlet of reaction tank. It was concluded that a management strategy of sewage is needed to prevent consuming organic substrate in the sewer.In addition, the controllability of intermittently aerated 2-tank activated sludge process for various influent organic load has been compared with A2/O process on the simulation. Some control strategies under the low organic substrate condition were examined on this simulator.