DOG-209FYS dissolved oxygen sensor uses fluorescence measurement of dissolved oxygen, blue light emitted by the phosphor layer, a fluorescent substance is excited to emit red light, and the fluorescent substance and the concentration of oxygen is inversely proportional to the time back to the ground state. The method uses a measurement of dissolved oxygen, no oxygen consumption measurement, the data is stable, reliable performance, there is no interference, installation and calibration simple. Widely used in sewage treatment plants each process, water plants, surface water, industrial process water production and waste water treatment, aquaculture and other industries on-line monitoring of DO.