Abstract: The decay heat inside the QM-400 storage room for dry type spent nuclear fuel at the Third Qinshan Nuclear Power Plant was investigated numerically. With using the commercial package FLUENT, a three dimensional computational fluid dynamics model was developed to evaluate the thermal performance of QM-400 storage room. The detailed simulation results for flow field, pressure and temperature distribution inside the storage room were provided. The characteristics of natural convection and heat transfer inside the storage room were explored and both of the surface temperature distributions for the storage tank and spent nuclear were predicted successfully. The current study can provide the optimization design information to enhance the thermal performance of dry type spent nuclear fuel storage room.