The invention relates to a method for detecting a dynamic specific oxygen utilization rate of an activated sludge system, belonging to a theory and a technology for enhancing a biological nitrogen removal process by activated sludge process. Aiming at the problems of a traditional method for measuring the oxygen utilization rate such as off-line measurement, hysteresis quality, no on-line measurement and on-line feedback, and the like, the invention provides a method for detecting the specific oxygen utilization rate of the activated sludge system with on-line measurement and on-line feedback. The invention has the following creative features that a programmable controller and a measuring system are used for on-line monitoring the specific oxygen utilization rate of the activated sludge and effectively representing a SBR technical biochemical reaction process; wherein, when the specific oxygen utilization rate is lower than a set value, the controller judges according to a feedback signal so as to transmit a control signal to a fan to stop aeration. The invention has the advantages of simple operation, sensitive response, etc. By detecting the index, the invention can timely feed back the operation information in the process of aerating, therefore establishing a theoretical base and a data support for realizing real-time control which uses the specific oxygen utilization rate as a parameter.