Abstract: Up to now the most of migration simulation of radionuclide in compacted backfill material was experimental in the lab. Against this problem, the long-term diffusion and migration of radionuclide Cs in compacted backfill material were simulated by using the migration of mathematic model with the experimental data and the migration mechanism of radionuclide. Effects of time, water velocity, distribution coefficient and dispersion coefficient on the migration and diffusion of Cs in compacted backfill material were also simulated. Preliminary research suggests that the migration of Cs in compacted backfill material is affected mainly by water velocity, distribution coefficient and dispersion coefficient. Compacted backfill material of 6 m thickness may be sufficient to prevent Cs from diffusion to environment in ten thousand years.