Abstract: By establishing the hydrodynamic model of Pacific Ocean, the dispersion pattern of nuclides in the relevant sea area after the occurrence of Fukushima nuclear leakage, the prediction of Fukushima nuclear sewage shipments discharge and the prediction of nuclear sewage discharge in the tunnel 1 km away from the coast were calculated. By comparing the calculated results with the actual measured values, it is found that the simulation results are in good agreement with the actual measured values, which proves the accuracy of the calculated results. The calculation results show that the nuclear contaminated water migrates with the sea current on the one hand and spreads on the other hand, and the area with higher radionuclide concentration migrates northward along the coastline and then spirals forward in the northeast direction. After the nuclear contaminated water is discharged by ship, the nuclides migrate slowly with the ocean current, basically presenting the axial diffusion centered on the discharge point. Affected by ocean currents, tides and diffusion, radionuclides in nuclear contaminated water gradually show a zonal distribution and migrate to the northeast direction, and reach the coastal area of Japan in about 15 days. Whether it is discharged at the coast, or 1 km away from the coast, radionuclides will quickly spread to the coast. As diffusion proceeds, radionuclides in nuclear contaminated water gradually show a zonal distribution affected by currents, tides and diffusion, and migrate in the northeast direction.