The oil-in-water emulsion of sea oil spills has caused serious harm to the ocean. The identification and quantitative analysis of oil-in-water emulsion is of great significance for treating marine pollution and restoring the marine environment. In recent years, some studies have conducted quantitative analysis on thinner emulsified oil spills, but there are rare in-depth studies on thicker emulsified oil spills. The fluorescence produced by the oil-in-water emulsion irradiated by the laser on the sea surface will begin to appear saturated under certain conditions and will not change anymore. This paper studies the spectral characteristics of the oil-in-water emulsion at this critical point of saturation and related ranges. According to the relationship between the optical power received by the LIF detection system and the BRRDF value, the fluorescence spectrum is simulated using the BRRDF model. The analysis uses Romashkino oil and Petrobaltic oil, representing dark opaque and bright transparent oil.A method for calculating the fluorescence intensity of thicker oil-in-water emulsions was proposed, and the thickness at which fluorescence saturation appeared in emulsions of two oils at different concentrations and emulsification times was calculated. Comparing the calculated results, it can be seen that the saturated thickness decreases with the increase of concentration and decreases with the increase of emulsification time. The analysis results show that for the oil-in-water emulsion of dark opaque oil in seawater, the fluorescence intensity received by LIF is usually saturated, so the thickness of the emulsion layer exceeding the saturation thickness cannot be judged by using the LIF system alone. A neural network with 4 layers of neurons was designed to verify the ability of the fluorescence spectrum near the saturation critical point to identify the emulsion concentration. The verification results show that as long as the oil-in-water emulsions of different concentrations reach or exceed the saturation thickness, the fluorescence spectrum has good discrimination ability, which can be used to distinguish the emulsions of different concentrations. For those samples far from the saturation thickness, fluorescence spectroscopy can distinguish whether the emulsion has reached saturation thickness. These experiments and conclusions will provide a reference for identifying and quantitatively analyzing thicker oil-in-water emulsions.