An oil spill accident happened in Tokyo Bay on 2 July 1997, About 1500 m(3) of crude oil was released on the sea surface from the Japanese tanker Diamond Grace. An oil spill model is applied to simulate the fate of spilled oil, The Lagrangian discrete-parcel method is used in the model, The model considers current advection, horizontal diffusion, mechanical spreading, evaporation, dissolution and entrainment in simulating the oil slick transformation. It can calculate the time evolution of the partition of spilled oil on the water surface, in the mater column and the sedimentation on the bottom, A continuous source at constant rate is set up as a tanker off the coast of Yokohama, The grid size is 1 km in the calculation domain. The residual flow simulated by a 3-D hydraulic model and observed wind data are used for advection, The simulated distribution of oil spreading agrees well with observations from satellite remote-sensing.