Characterization of biochemical oxygen demand（BOD）is a comprehensive index which shows the degree of organic pollution of water.The index is widely used in operation control of water test and wastewater treatment plant.The operating principle of electrical control system of BOD rapid determination instrument using biosensor is outlined.The purpose and significance of the system is introduced briefly.Hardware configuration and software design of the instrument are detailed.User-friendly man-machine interface is designed for the window mode in order to achieve the function of automatic detection of real-time display to meet the requirements of quick and accurate test of organic pollution.It’s important for the evaluation of water quality

rational use of water resources and water efficiency.