Abstract: The discharge of produced water from offshore oil platform is one of the important sources of marine environmental pollution. While manual sampling and analysis are still the main methods,it is urgent to study the online monitoring technology of oil in water for production water of offshore oil platform. In this paper, oil-bearing produced water samples from different offshore oilfields were taken as the research object, and were tested by both near-ultraviolet and deep ultraviolet oil sensors with different excitation wavelengths. The fluorescence spectral characteristics of oily water samples were studied and the correlation between fluorescence signal and oil content was established. The near-ultraviolet oil sensor with an excitation wavelength of 360 nm can be applied to detect oil concentration in produced water with density range from light oil to heavy oil, but the sensitivity to low concentration is low; The deep ultraviolet oil sensor with an excitation wavelength of 255 nm is ideal for produced water from non-heavy oil oilfields except heavy oil, and fluorescence quenching is easy to occur prematurely in higher concentrations. As a result, the oil type and daily detection concentration range should be comprehensively considered to select the wavelength of the oil sensor for online monitoring of produced water in offshore platforms. The outcomes of this paper can provide a reference for the rapid detection of oil spills at sea.