There are two kinds of oil spills on the sea surface: non-emulsification and emulsification. The scientific detection and evaluation of oil spills on the sea are helpful to the recovery and treatment of oil spill pollution and formulate of an emergency plan. For non-emulsified oil spill, mainly exists in the form of oil film, and its thickness becomes an important evaluation index of oil spill; for emulsion spills they mainly exist in the form of water in oil or oil in water, and the oil-water ratio can be used as the basis for evaluation. Laser-induced fluorescence (LIF) technology is considered one of the most effective methods for oil spill detection. Oil film thickness inversion based on LIF detection technology has seen the relevant research algorithm, but there is no corresponding quantitative method of oil spill on the sea surface, and the oil spill on the sea surface will bring greater harm to the marine environment. Therefore, it is an urgent task to analyze and study the information on emulsion oil spills on the sea surface. Based on the detection mechanism of LIF system, an equivalent estimation model for water in oil emulsion spillage is proposed: Firstly, the oil spill of continuous phase in water in oil is regarded as an oil film with the same optical properties, the water droplets of all dispersed phases are regarded as a whole, which is equivalent to a thin water layer, in order to keep the equivalent model consistent with the external environment of the actual emulsion, an oil surface is covered on the thin water layer, so that the estimation of oil spill volume of water in oil emulsion is converted into the calculation of equivalent oil film thickness; Secondly, according to the radiation transmission process of light, the equation of fluorescence information that the system can receive is established, and the calculation formula of oil film thickness is sorted out. That is, based on knowing the oil type, the corresponding thickness value can be obtained by substituting the fluorescence intensity value measured by the system, and then the oil spill amount can be estimated. The paper also analyzes the error caused by the equivalent model through an example to verify the applicability and effectiveness of the estimation method under the equivalent model. That is, when the oil content and thickness of water in oil emulsion are in a certain range, there is a small error between the actual oil spill thickness and the equivalent oil film thickness. The equivalent treatment method studied in this paper can provide a new method for estimating emulsified oil spills on the sea surface, which has important guiding significance and certain innovative value for solving this problem.