Abstract: The research object is HI-STORM 100 spent fuel dry storage facility internal loading AFA-3G fuel assembly in this paper. Using the MCNP (Monte Carlo N Particle Transport Code) code, neutron dose, γ dose and total dose were calculated under different conditions, such as cooling time, locations. Results show that the value of gamma dose rate, neutron dose rate and total dose rate reduce gradually with the extension of the cooling time. The maximum radiation dose rate is about 2.47 mSv/h. So it is a high radiation area that should not be entered. In order to meet the purpose of as low as reasonably achievable, it is recommended to take relevant measures such as increasing the thickness of shielding, or setting up control areas, etc.