In this paper, coupling ocean and oil spill model, an oil spill trajectory forecast model for Yangtze Estuary was developed. The ocean model can better simulate the sea surface current field. Oil spill model by using oil particles tracking method of random walk and Lagrange, can quickly predict the drift trajectory and swept area of oil particles. Result shows that oil particle distribution and swept areas in spring tide are greater than those in neap tide. Spilled oil particles in the south branch would drift to south and north channels and south and north passages. The greatest harms to ecological environment will affect water intake of Chenhang and Qingchaosha reservoirs, and has potential ecological harm to the Chinese sturgeon and Jiuduansha wetland reserve; Spilled oil particles in the north branch are mainly distributed in the north branch channel and both shores. If oil spill spot is in upper north branch, oil particles would flow backward into the south branch channel, will do great harm to ecology; spilled oil particles in south channel would drift to the north and south passage, and will not harm two reservoirs and Chinese sturgeon reserve, but will do potential harm to Jiuduansha reserves; Spilled oil particles in the north channel would drift to Chongming island out sea, and diffusion range is very large, only harming the Chinese sturgeon reserve.