The prediction of radionuclide diffusion is one of the indispensable factors for the nuclear emergency decision. So far, it is still short of an accurate simulation for the radionuclide diffusion in a spent nuclear fuel storage. Compared with the radionuclide diffusion in atmosphere, the airflow inside a dry-storage is always in turbulent state with a ventilation system, and diffusion process of radionuclide in the spent fuel dry storage is very complex. Therefore, a choice of an appropriate model is key point to estimate radionuclide dispersion in the dry storage. In this paper, the radionuclide concentration equation with the consideration of room wind field, wall condition and the features of radionuclide is updated to simulate the radionuclide dispersion in the spent fuel dry-storage with four vents. A three-dimensional model of radioactive concentration is obtained based on the standard k-epsilon turbulence model. The simulation results reveal that the standard k-epsilon turbulence model combined with updated radionuclide concentration equation gives a reasonable description for radionuclide diffusion under accident condition so as to provide more actual information for early emergency and consequence assessment.