Abstract: In order to effectively control internal recirculation flow in A/O (anoxic/oxic) nitrogen removal process, i.e., to make nitrate produced in aerobic zone flow to anoxic zone so as to achieve the effective removal of oxygen, according to the analysis about utilization efficiency of the influent biodegradable COD for nitrate removal and denitrification rate influence factors, the internal recirculation flow control strategy is built, that is, maintaining nitrate concentration at the end of anoxic zone at the best setpoint 2.5 mg/L by controlling nitrate recirculation flow. Studies show that the setpoint appears to be robust towards variation in the influent characteristics; effluent nitrate and total nitrogen concentration can be remained the lowest value, and markedly reduce energy consumption of internal recirculation. In order to achieve intelligent control of wastewater treatment plants, the internal recirculation flow fuzzy controller is developed.