Fluorescence Method Dissolved Oxygen Analyzer is based on the principle of fluorescence quenching, blue light irradiates to the fluorescent material to make the fluorescent material excitate red light, because the oxygen molecules can take away the energy (quenching reaction), the time and intensity of red light and the concentration of oxygen molecules are inversely proportional. By measuring, the phase difference is excitated between the red light and the reference light, then to calculate the concentration of oxygen molecules by corresponding to the internal calibration value. By adopting innovative new fluorescent technology, no membrane and electrolyte is needed, almost no maintenance, excellent performance, easy to operate, no oxygen consumed, can be applied to any occasion, including those low water cycle.