The work aims to study the heat transfer characteristics of transportable reactors during the shutdown and cooling process before transportation and the maximum temperature on the surface of the metal container outside the reactor, so as to meet the requirements of GB 11806-2019 Regulations for the Safe Transport of Radioactive Materials .The transportation heat transfer process of a mobile reactor with a rated thermal power of 15 MW under the existing design conditions was simulated by Fluent simulation software, and the influence of the residual decay heat of the reactor on the surface temperature of the tank was calculated under other conditions. After modeling and calculation, it was concluded that the maximum temperature on the surface of the metal container of the mobile reactor during transportation was 69 ℃ under the existing design conditions, and the maximum temperature of the surface of the tank was 83.5 ℃ when the residual decay heat of the reactor was 0.1 MW, which was close to the requirement of GB 11806-2019 that the temperature of the accessible surface of radioactive material transport container should not exceed 85 ℃. In conclusion,combined with the correspondence between the shutdown cooling time of the high-temperature gas-cooled reactor and the residual thermal power of the reactor, it is concluded that when the thermal power of the reactor reaches 13.9 MW, only one day of shutdown cooling is needed to meet the relevant requirements of GB 11806-2019. When the thermal power of the reactor reaches 24 MW, it takes 10 days to cool. And when the thermal power of the reactor exceeds 24 MW, only additional cooling methods can be used to cool the reactor to meet relevant requirements of GB 11806-2019.