With the development of marine resources and marine transportation, oil spill accidents occur frequently which threaten the marine ecological environment and human life. In this paper, an oil spill model was established. With discretizing two-dimensional shallow equation by finite element method, the oil spill hydrodynamic-numerical model was established. As the water boundary condition was defined by harmonic analysis method, the model was verified by measure tidal level data. The boundary treatment method of multiple islands and complex shoreline was proposed. Monte Carlo Method is used to simulate the diffusion and drift of oil spill, Euler-Lagrange method is used to track the film centroid and oil film boundary, and a random number was added to indicate the randomness of oil film expansion. The diffusion drift of oil film was verified by flume test. At the same time, this model considered the weathering process of evaporation, emulsification and entrainment of oil spills, and calculated the onshore adsorption of oil spills. The model is applied to Daya Bay, South China Sea, the oil spill behavior and destination under different residual currents were simulated and calculated, which provides a theoretical basis for the prevention and emergency treatment of oil spill accidents.